[PATCH net-next v5 0/2] net: wwan: qcom_bam_dmux: Add restricted DMA pool support

[PATCH net-next v5 0/2] net: wwan: qcom_bam_dmux: Add restricted DMA pool support

[Vishnu Santhosh]

Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
domain with restricted access to system memory. BAM-DMUX DMA mappings
and BAM descriptor FIFOs must therefore be constrained to a designated
memory region that can be shared with the modem. Accesses outside that
region can trigger an XPU violation.

Add memory-region and qcom,vmid properties to the BAM-DMUX binding, and
a qcom,shikra-bam-dmux compatible that requires them. When qcom,vmid is
present, the driver SCM-assigns the entire restricted DMA pool to the
local and remote execution environments before requesting the DMA
channels.

The restricted pool then contains the BAM-DMUX mappings. When the BAM DMA
controller references the same pool, its descriptor FIFOs are covered by
the assignment as well.

A related binding change allows the BAM DMA controller to use the same
restricted pool for descriptor FIFO allocations:

https://lore.kernel.org/all/20261021-qcom-bam-dma-vmid-ext-v3-1-299355e8dd3b@oss.qualcomm.com/
("dt-bindings: dma: qcom,bam-dma: Allow memory-region property")

Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
---
Changes in v5:
- Drop the redundant restricted-dma-pool compatible check, since
  is_swiotlb_for_alloc() already covers it (Loic)
- Link to v4: https://lore.kernel.org/r/20261103-qcom-bam-dmux-vmid-ext-v4-0-3690cc5ca0fd@oss.qualcomm.com

Changes in v4:
- Decide the pool reclaim on the remote power vote after disabling the
  PC IRQ (Sashiko)
- Link to v3: https://lore.kernel.org/r/20261021-qcom-bam-dmux-vmid-ext-v3-0-cedd1f681102@oss.qualcomm.com

Changes in v3:
- dt-bindings: Add qcom,shikra-bam-dmux, with qcom,bam-dmux as fallback,
  and require memory-region and qcom,vmid for it (Krzysztof)
- dt-bindings: Drop minItems from qcom,vmid (Krzysztof)
- dt-bindings: Drop the example changes (Krzysztof)
- dt-bindings: Drop the statement about the local VMID from the
  qcom,vmid description (Sashiko)
- Reuse remove() on late probe failure, since the PC IRQ may already
  have powered up the RX path (Sashiko)
- Skip the pool reclaim when the remote did not acknowledge the
  power-down (Sashiko)
- Fail probe if the restricted pool is not attached to the device
  (Sashiko)
- Link to v2: https://lore.kernel.org/r/20260920-qcom-bam-dmux-vmid-ext-v2-0-ef5ca2178378@oss.qualcomm.com

Changes in v2:
- Replace the Shikra-specific compatible and coherent RX allocation with
  memory-region and qcom,vmid properties.
- Use a restricted DMA pool for BAM-DMUX mappings and BAM descriptor FIFOs.
- SCM-assign the complete pool before requesting the DMA channels.
- Validate the remote VMID and restricted DMA pool configuration.
- Link to v1: https://lore.kernel.org/r/20260714-qcom-bam-dmux-vmid-ext-v1-0-3f29da7cca76@oss.qualcomm.com

---
Vishnu Santhosh (2):
      dt-bindings: net: qcom,bam-dmux: Add memory-region and qcom,vmid properties
      net: wwan: qcom_bam_dmux: Assign restricted DMA pool to remote processor

 .../devicetree/bindings/net/qcom,bam-dmux.yaml     |  36 ++++++-
 drivers/net/wwan/Kconfig                           |   1 +
 drivers/net/wwan/qcom_bam_dmux.c                   | 108 ++++++++++++++++++++-
 3 files changed, 142 insertions(+), 3 deletions(-)
---
base-commit: 7b6ab4dbc156e2f96419715130b3d5738a306c93
change-id: 20260714-qcom-bam-dmux-vmid-ext-d9289db310c1

Best regards,
-- 
Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>

[PATCH net-next v5 1/2] dt-bindings: net: qcom,bam-dmux: Add memory-region and qcom,vmid properties

[Vishnu Santhosh]

Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
domain with restricted access to system memory. BAM-DMUX DMA mappings
must therefore be constrained to a designated region that can be shared
with the modem.

Add an optional memory-region property to reference a restricted DMA
pool used for BAM-DMUX mappings, and a qcom,vmid property to identify the
remote execution environment that is granted access to the pool through
SCM.

Require memory-region whenever qcom,vmid is specified.

Add the qcom,shikra-bam-dmux compatible, with qcom,bam-dmux as fallback,
and require both properties for it.

Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
---
 .../devicetree/bindings/net/qcom,bam-dmux.yaml     | 36 +++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml b/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
index 33746c238513d72366bc52359fb10f275475b331..f7388d24c8612b5a99d5d0e66cfbe2de3b1c9e0d 100644
--- a/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
+++ b/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
@@ -22,7 +22,11 @@ description: |
 
 properties:
   compatible:
-    const: qcom,bam-dmux
+    oneOf:
+      - const: qcom,bam-dmux
+      - items:
+          - const: qcom,shikra-bam-dmux
+          - const: qcom,bam-dmux
 
   interrupts:
     description:
@@ -72,6 +76,22 @@ properties:
       - const: tx
       - const: rx
 
+  memory-region:
+    maxItems: 1
+    description:
+      Phandle to a reserved-memory node compatible with restricted-dma-pool.
+      The BAM-DMUX device uses the pool for DMA mappings.
+
+  qcom,vmid:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    maxItems: 1
+    items:
+      minimum: 1
+      maximum: 63
+    description:
+      VMID of the remote execution environment that is granted access to the
+      restricted DMA pool through SCM.
+
 required:
   - compatible
   - interrupts
@@ -81,6 +101,20 @@ required:
   - dmas
   - dma-names
 
+dependencies:
+  qcom,vmid: [ memory-region ]
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: qcom,shikra-bam-dmux
+    then:
+      required:
+        - memory-region
+        - qcom,vmid
+
 additionalProperties: false
 
 examples:

-- 
2.34.1

[PATCH net-next v5 2/2] net: wwan: qcom_bam_dmux: Assign restricted DMA pool to remote processor

[Vishnu Santhosh]

Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
domain with restricted access to system memory. BAM-DMUX DMA mappings
and BAM descriptor FIFOs must therefore be constrained to a designated
memory region that can be shared with the modem. Accesses outside that
region can trigger an XPU violation.

When qcom,vmid is present, require a restricted DMA pool and assign the
entire pool to both the local and remote execution environments before
requesting the DMA channels.

This ensures that BAM-DMUX mappings are within the assigned region. When
the BAM DMA controller references the same pool, its descriptor FIFOs
are covered by the assignment as well.

Track the assigned execution environments explicitly and reclaim the
pool for the local environment after DMA channels and mappings are
released during remove or probe error cleanup. Skip the reclaim and
leave the pool assigned if the remote side still holds its power vote,
since it may still access the pool.

Fail probing when restricted DMA pool support is unavailable, when the
VMID property is malformed, when memory-region is missing, or when the
restricted DMA pool is not attached to the device.

Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
---
 drivers/net/wwan/Kconfig         |   1 +
 drivers/net/wwan/qcom_bam_dmux.c | 108 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 107 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wwan/Kconfig b/drivers/net/wwan/Kconfig
index 958dbc7347fa84ee869439bf8b503037faab8bef..1b133c56231615269698140187ca3141dfe48dbf 100644
--- a/drivers/net/wwan/Kconfig
+++ b/drivers/net/wwan/Kconfig
@@ -65,6 +65,7 @@ config MHI_WWAN_MBIM
 config QCOM_BAM_DMUX
 	tristate "Qualcomm BAM-DMUX WWAN network driver"
 	depends on (DMA_ENGINE && PM && QCOM_SMEM_STATE) || COMPILE_TEST
+	select QCOM_SCM
 	help
 	  The BAM Data Multiplexer provides access to the network data channels
 	  of modems integrated into many older Qualcomm SoCs, e.g. Qualcomm
diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
index cc6ace8d64371eb8d00c638a39b234ee540b83c9..0e7ad62f8b4e059264e89837f296ee13c0c31c9b 100644
--- a/drivers/net/wwan/qcom_bam_dmux.c
+++ b/drivers/net/wwan/qcom_bam_dmux.c
@@ -9,14 +9,17 @@
 #include <linux/completion.h>
 #include <linux/dma-mapping.h>
 #include <linux/dmaengine.h>
+#include <linux/firmware/qcom/qcom_scm.h>
 #include <linux/if_arp.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/netdevice.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/soc/qcom/smem_state.h>
 #include <linux/spinlock.h>
+#include <linux/swiotlb.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 #include <net/pkt_sched.h>
@@ -75,6 +78,9 @@ struct bam_dmux {
 	struct completion pc_ack_completion;
 
 	struct dma_chan *rx, *tx;
+	phys_addr_t dma_pool_base;
+	size_t dma_pool_size;
+	u64 dma_pool_perms;
 	struct bam_dmux_skb_dma rx_skbs[BAM_DMUX_NUM_SKB];
 	struct bam_dmux_skb_dma tx_skbs[BAM_DMUX_NUM_SKB];
 	spinlock_t tx_lock; /* Protect tx_skbs, tx_next_skb */
@@ -762,6 +768,90 @@ static int __maybe_unused bam_dmux_runtime_resume(struct device *dev)
 	return 0;
 }
 
+static int bam_dmux_assign_dma_pool(struct bam_dmux *dmux)
+{
+	struct device *dev = dmux->dev;
+	struct device_node *rmem_np;
+	struct reserved_mem *rmem;
+	struct qcom_scm_vmperm dst[2];
+	u64 src = BIT_ULL(QCOM_SCM_VMID_HLOS);
+	u32 vmid;
+	int ret;
+
+	if (!of_property_present(dev->of_node, "qcom,vmid"))
+		return 0;
+
+	ret = of_property_read_u32(dev->of_node, "qcom,vmid", &vmid);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to read qcom,vmid\n");
+	if (vmid == QCOM_SCM_VMID_HLOS || vmid >= BITS_PER_TYPE(u64))
+		return dev_err_probe(dev, -EINVAL, "Invalid qcom,vmid %u\n", vmid);
+
+	if (!IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL))
+		return dev_err_probe(dev, -EOPNOTSUPP,
+				     "qcom,vmid requires DMA_RESTRICTED_POOL\n");
+
+	rmem_np = of_parse_phandle(dev->of_node, "memory-region", 0);
+	if (!rmem_np)
+		return dev_err_probe(dev, -EINVAL,
+					     "qcom,vmid requires memory-region\n");
+
+	rmem = of_reserved_mem_lookup(rmem_np);
+	of_node_put(rmem_np);
+	if (!rmem)
+		return dev_err_probe(dev, -EINVAL,
+					     "Failed to look up restricted DMA pool\n");
+
+	if (!is_swiotlb_for_alloc(dev))
+		return dev_err_probe(dev, -EINVAL,
+				     "Restricted DMA pool not attached\n");
+
+	if (!qcom_scm_is_available())
+		return -EPROBE_DEFER;
+
+	dst[0].vmid = QCOM_SCM_VMID_HLOS;
+	dst[0].perm = QCOM_SCM_PERM_RW;
+	dst[1].vmid = vmid;
+	dst[1].perm = QCOM_SCM_PERM_RW;
+
+	ret = qcom_scm_assign_mem(rmem->base, rmem->size, &src, dst,
+				  ARRAY_SIZE(dst));
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "SCM assign restricted DMA pool failed\n");
+
+	dmux->dma_pool_base = rmem->base;
+	dmux->dma_pool_size = rmem->size;
+	/* Track the destination VMIDs explicitly for the reclaim operation. */
+	dmux->dma_pool_perms = BIT_ULL(QCOM_SCM_VMID_HLOS) | BIT_ULL(vmid);
+
+	return 0;
+}
+
+static void bam_dmux_reclaim_dma_pool(struct bam_dmux *dmux)
+{
+	struct qcom_scm_vmperm hlos = {
+		.vmid = QCOM_SCM_VMID_HLOS,
+		.perm = QCOM_SCM_PERM_RW,
+	};
+	u64 src = dmux->dma_pool_perms;
+	int ret;
+
+	if (!dmux->dma_pool_perms)
+		return;
+
+	ret = qcom_scm_assign_mem(dmux->dma_pool_base, dmux->dma_pool_size, &src,
+				  &hlos, 1);
+	if (ret) {
+		dev_err(dmux->dev, "SCM reclaim restricted DMA pool failed: %d\n", ret);
+		return;
+	}
+
+	dmux->dma_pool_perms = 0;
+}
+
+static void bam_dmux_remove(struct platform_device *pdev);
+
 static int bam_dmux_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -796,6 +886,10 @@ static int bam_dmux_probe(struct platform_device *pdev)
 				     "Failed to get pc-ack state\n");
 	dmux->pc_ack_mask = BIT(bit);
 
+	ret = bam_dmux_assign_dma_pool(dmux);
+	if (ret)
+		return ret;
+
 	init_waitqueue_head(&dmux->pc_wait);
 	init_completion(&dmux->pc_ack_completion);
 	complete_all(&dmux->pc_ack_completion);
@@ -829,8 +923,11 @@ static int bam_dmux_probe(struct platform_device *pdev)
 
 	ret = irq_get_irqchip_state(dmux->pc_irq, IRQCHIP_STATE_LINE_LEVEL,
 				    &dmux->pc_state);
-	if (ret)
-		goto err_disable_pm;
+	if (ret) {
+		/* The PC IRQ may already have powered up the RX path */
+		bam_dmux_remove(pdev);
+		return ret;
+	}
 
 	/* Check if remote finished initialization before us */
 	if (dmux->pc_state) {
@@ -845,6 +942,7 @@ static int bam_dmux_probe(struct platform_device *pdev)
 err_disable_pm:
 	pm_runtime_disable(dev);
 	pm_runtime_dont_use_autosuspend(dev);
+	bam_dmux_reclaim_dma_pool(dmux);
 	return ret;
 }
 
@@ -879,6 +977,12 @@ static void bam_dmux_remove(struct platform_device *pdev)
 	disable_irq(dmux->pc_irq);
 	bam_dmux_power_off(dmux);
 	bam_dmux_free_skbs(dmux->tx_skbs, DMA_TO_DEVICE);
+
+	/* The remote side may still access the pool if it holds its power vote */
+	if (!dmux->pc_state)
+		bam_dmux_reclaim_dma_pool(dmux);
+	else if (dmux->dma_pool_perms)
+		dev_warn(dev, "Leaving restricted DMA pool assigned to remote\n");
 }
 
 static const struct dev_pm_ops bam_dmux_pm_ops = {

-- 
2.34.1

Re: [PATCH net-next v5 2/2] net: wwan: qcom_bam_dmux: Assign restricted DMA pool to remote processor

[Loic Poulain]

On Thu, Nov 5, 2026 at 11:42 AM Vishnu Santhosh
<vishnu.santhosh@oss.qualcomm.com> wrote:
>
> Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
> domain with restricted access to system memory. BAM-DMUX DMA mappings
> and BAM descriptor FIFOs must therefore be constrained to a designated
> memory region that can be shared with the modem. Accesses outside that
> region can trigger an XPU violation.
>
> When qcom,vmid is present, require a restricted DMA pool and assign the
> entire pool to both the local and remote execution environments before
> requesting the DMA channels.
>
> This ensures that BAM-DMUX mappings are within the assigned region. When
> the BAM DMA controller references the same pool, its descriptor FIFOs
> are covered by the assignment as well.
>
> Track the assigned execution environments explicitly and reclaim the
> pool for the local environment after DMA channels and mappings are
> released during remove or probe error cleanup. Skip the reclaim and
> leave the pool assigned if the remote side still holds its power vote,
> since it may still access the pool.
>
> Fail probing when restricted DMA pool support is unavailable, when the
> VMID property is malformed, when memory-region is missing, or when the
> restricted DMA pool is not attached to the device.
>
> Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
> Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
> Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
> ---
>  drivers/net/wwan/Kconfig         |   1 +
>  drivers/net/wwan/qcom_bam_dmux.c | 108 ++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 107 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wwan/Kconfig b/drivers/net/wwan/Kconfig
> index 958dbc7347fa84ee869439bf8b503037faab8bef..1b133c56231615269698140187ca3141dfe48dbf 100644
> --- a/drivers/net/wwan/Kconfig
> +++ b/drivers/net/wwan/Kconfig
> @@ -65,6 +65,7 @@ config MHI_WWAN_MBIM
>  config QCOM_BAM_DMUX
>         tristate "Qualcomm BAM-DMUX WWAN network driver"
>         depends on (DMA_ENGINE && PM && QCOM_SMEM_STATE) || COMPILE_TEST
> +       select QCOM_SCM
>         help
>           The BAM Data Multiplexer provides access to the network data channels
>           of modems integrated into many older Qualcomm SoCs, e.g. Qualcomm
> diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
> index cc6ace8d64371eb8d00c638a39b234ee540b83c9..0e7ad62f8b4e059264e89837f296ee13c0c31c9b 100644
> --- a/drivers/net/wwan/qcom_bam_dmux.c
> +++ b/drivers/net/wwan/qcom_bam_dmux.c
> @@ -9,14 +9,17 @@
>  #include <linux/completion.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/dmaengine.h>
> +#include <linux/firmware/qcom/qcom_scm.h>
>  #include <linux/if_arp.h>
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
>  #include <linux/netdevice.h>
> +#include <linux/of_reserved_mem.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/soc/qcom/smem_state.h>
>  #include <linux/spinlock.h>
> +#include <linux/swiotlb.h>
>  #include <linux/wait.h>
>  #include <linux/workqueue.h>
>  #include <net/pkt_sched.h>
> @@ -75,6 +78,9 @@ struct bam_dmux {
>         struct completion pc_ack_completion;
>
>         struct dma_chan *rx, *tx;
> +       phys_addr_t dma_pool_base;
> +       size_t dma_pool_size;
> +       u64 dma_pool_perms;
>         struct bam_dmux_skb_dma rx_skbs[BAM_DMUX_NUM_SKB];
>         struct bam_dmux_skb_dma tx_skbs[BAM_DMUX_NUM_SKB];
>         spinlock_t tx_lock; /* Protect tx_skbs, tx_next_skb */
> @@ -762,6 +768,90 @@ static int __maybe_unused bam_dmux_runtime_resume(struct device *dev)
>         return 0;
>  }
>
> +static int bam_dmux_assign_dma_pool(struct bam_dmux *dmux)
> +{
> +       struct device *dev = dmux->dev;
> +       struct device_node *rmem_np;
> +       struct reserved_mem *rmem;
> +       struct qcom_scm_vmperm dst[2];
> +       u64 src = BIT_ULL(QCOM_SCM_VMID_HLOS);
> +       u32 vmid;
> +       int ret;
> +
> +       if (!of_property_present(dev->of_node, "qcom,vmid"))
> +               return 0;
> +
> +       ret = of_property_read_u32(dev->of_node, "qcom,vmid", &vmid);
> +       if (ret)
> +               return dev_err_probe(dev, ret, "Failed to read qcom,vmid\n");
> +       if (vmid == QCOM_SCM_VMID_HLOS || vmid >= BITS_PER_TYPE(u64))
> +               return dev_err_probe(dev, -EINVAL, "Invalid qcom,vmid %u\n", vmid);
> +
> +       if (!IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL))
> +               return dev_err_probe(dev, -EOPNOTSUPP,
> +                                    "qcom,vmid requires DMA_RESTRICTED_POOL\n");
> +
> +       rmem_np = of_parse_phandle(dev->of_node, "memory-region", 0);
> +       if (!rmem_np)
> +               return dev_err_probe(dev, -EINVAL,
> +                                            "qcom,vmid requires memory-region\n");
> +
> +       rmem = of_reserved_mem_lookup(rmem_np);
> +       of_node_put(rmem_np);
> +       if (!rmem)
> +               return dev_err_probe(dev, -EINVAL,
> +                                            "Failed to look up restricted DMA pool\n");
> +
> +       if (!is_swiotlb_for_alloc(dev))
> +               return dev_err_probe(dev, -EINVAL,
> +                                    "Restricted DMA pool not attached\n");
> +
> +       if (!qcom_scm_is_available())
> +               return -EPROBE_DEFER;
> +
> +       dst[0].vmid = QCOM_SCM_VMID_HLOS;
> +       dst[0].perm = QCOM_SCM_PERM_RW;
> +       dst[1].vmid = vmid;
> +       dst[1].perm = QCOM_SCM_PERM_RW;
> +
> +       ret = qcom_scm_assign_mem(rmem->base, rmem->size, &src, dst,
> +                                 ARRAY_SIZE(dst));
> +       if (ret)
> +               return dev_err_probe(dev, ret,
> +                                    "SCM assign restricted DMA pool failed\n");
> +
> +       dmux->dma_pool_base = rmem->base;
> +       dmux->dma_pool_size = rmem->size;
> +       /* Track the destination VMIDs explicitly for the reclaim operation. */
> +       dmux->dma_pool_perms = BIT_ULL(QCOM_SCM_VMID_HLOS) | BIT_ULL(vmid);
> +
> +       return 0;
> +}
> +
> +static void bam_dmux_reclaim_dma_pool(struct bam_dmux *dmux)
> +{
> +       struct qcom_scm_vmperm hlos = {
> +               .vmid = QCOM_SCM_VMID_HLOS,
> +               .perm = QCOM_SCM_PERM_RW,
> +       };
> +       u64 src = dmux->dma_pool_perms;
> +       int ret;
> +
> +       if (!dmux->dma_pool_perms)
> +               return;
> +
> +       ret = qcom_scm_assign_mem(dmux->dma_pool_base, dmux->dma_pool_size, &src,
> +                                 &hlos, 1);
> +       if (ret) {
> +               dev_err(dmux->dev, "SCM reclaim restricted DMA pool failed: %d\n", ret);
> +               return;
> +       }
> +
> +       dmux->dma_pool_perms = 0;
> +}
> +
> +static void bam_dmux_remove(struct platform_device *pdev);
> +
>  static int bam_dmux_probe(struct platform_device *pdev)
>  {
>         struct device *dev = &pdev->dev;
> @@ -796,6 +886,10 @@ static int bam_dmux_probe(struct platform_device *pdev)
>                                      "Failed to get pc-ack state\n");
>         dmux->pc_ack_mask = BIT(bit);
>
> +       ret = bam_dmux_assign_dma_pool(dmux);
> +       if (ret)
> +               return ret;
> +
>         init_waitqueue_head(&dmux->pc_wait);
>         init_completion(&dmux->pc_ack_completion);
>         complete_all(&dmux->pc_ack_completion);
> @@ -829,8 +923,11 @@ static int bam_dmux_probe(struct platform_device *pdev)
>
>         ret = irq_get_irqchip_state(dmux->pc_irq, IRQCHIP_STATE_LINE_LEVEL,
>                                     &dmux->pc_state);
> -       if (ret)
> -               goto err_disable_pm;
> +       if (ret) {
> +               /* The PC IRQ may already have powered up the RX path */
> +               bam_dmux_remove(pdev);

it's still unclear in the comment and commit message why we can't go
with err_disable_pm?

> +               return ret;
> +       }
>
>         /* Check if remote finished initialization before us */
>         if (dmux->pc_state) {
> @@ -845,6 +942,7 @@ static int bam_dmux_probe(struct platform_device *pdev)
>  err_disable_pm:
>         pm_runtime_disable(dev);
>         pm_runtime_dont_use_autosuspend(dev);
> +       bam_dmux_reclaim_dma_pool(dmux);
>         return ret;
>  }
>
> @@ -879,6 +977,12 @@ static void bam_dmux_remove(struct platform_device *pdev)
>         disable_irq(dmux->pc_irq);
>         bam_dmux_power_off(dmux);
>         bam_dmux_free_skbs(dmux->tx_skbs, DMA_TO_DEVICE);
> +
> +       /* The remote side may still access the pool if it holds its power vote */
> +       if (!dmux->pc_state)
> +               bam_dmux_reclaim_dma_pool(dmux);
> +       else if (dmux->dma_pool_perms)
> +               dev_warn(dev, "Leaving restricted DMA pool assigned to remote\n");
>  }
>
>  static const struct dev_pm_ops bam_dmux_pm_ops = {
>
> --
> 2.34.1
>

Re: [PATCH net-next v5 2/2] net: wwan: qcom_bam_dmux: Assign restricted DMA pool to remote processor

[Vishnu Santhosh]

On 05-11-2026 07:51 pm, Loic Poulain wrote:
> On Thu, Nov 5, 2026 at 11:42 AM Vishnu Santhosh
> <vishnu.santhosh@oss.qualcomm.com> wrote:
>> Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
>> domain with restricted access to system memory. BAM-DMUX DMA mappings
>> and BAM descriptor FIFOs must therefore be constrained to a designated
>> memory region that can be shared with the modem. Accesses outside that
>> region can trigger an XPU violation.
>>
>> When qcom,vmid is present, require a restricted DMA pool and assign the
>> entire pool to both the local and remote execution environments before
>> requesting the DMA channels.
>>
>> This ensures that BAM-DMUX mappings are within the assigned region. When
>> the BAM DMA controller references the same pool, its descriptor FIFOs
>> are covered by the assignment as well.
>>
>> Track the assigned execution environments explicitly and reclaim the
>> pool for the local environment after DMA channels and mappings are
>> released during remove or probe error cleanup. Skip the reclaim and
>> leave the pool assigned if the remote side still holds its power vote,
>> since it may still access the pool.
>>
>> Fail probing when restricted DMA pool support is unavailable, when the
>> VMID property is malformed, when memory-region is missing, or when the
>> restricted DMA pool is not attached to the device.
>>
>> Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
>> Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
>> Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
>> ---
>>   drivers/net/wwan/Kconfig         |   1 +
>>   drivers/net/wwan/qcom_bam_dmux.c | 108 ++++++++++++++++++++++++++++++++++++++-
>>   2 files changed, 107 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/wwan/Kconfig b/drivers/net/wwan/Kconfig
>> index 958dbc7347fa84ee869439bf8b503037faab8bef..1b133c56231615269698140187ca3141dfe48dbf 100644
>> --- a/drivers/net/wwan/Kconfig
>> +++ b/drivers/net/wwan/Kconfig
>> @@ -65,6 +65,7 @@ config MHI_WWAN_MBIM
>>   config QCOM_BAM_DMUX
>>          tristate "Qualcomm BAM-DMUX WWAN network driver"
>>          depends on (DMA_ENGINE && PM && QCOM_SMEM_STATE) || COMPILE_TEST
>> +       select QCOM_SCM
>>          help
>>            The BAM Data Multiplexer provides access to the network data channels
>>            of modems integrated into many older Qualcomm SoCs, e.g. Qualcomm
>> diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
>> index cc6ace8d64371eb8d00c638a39b234ee540b83c9..0e7ad62f8b4e059264e89837f296ee13c0c31c9b 100644
>> --- a/drivers/net/wwan/qcom_bam_dmux.c
>> +++ b/drivers/net/wwan/qcom_bam_dmux.c
>> @@ -9,14 +9,17 @@
>>   #include <linux/completion.h>
>>   #include <linux/dma-mapping.h>
>>   #include <linux/dmaengine.h>
>> +#include <linux/firmware/qcom/qcom_scm.h>
>>   #include <linux/if_arp.h>
>>   #include <linux/interrupt.h>
>>   #include <linux/module.h>
>>   #include <linux/netdevice.h>
>> +#include <linux/of_reserved_mem.h>
>>   #include <linux/platform_device.h>
>>   #include <linux/pm_runtime.h>
>>   #include <linux/soc/qcom/smem_state.h>
>>   #include <linux/spinlock.h>
>> +#include <linux/swiotlb.h>
>>   #include <linux/wait.h>
>>   #include <linux/workqueue.h>
>>   #include <net/pkt_sched.h>
>> @@ -75,6 +78,9 @@ struct bam_dmux {
>>          struct completion pc_ack_completion;
>>
>>          struct dma_chan *rx, *tx;
>> +       phys_addr_t dma_pool_base;
>> +       size_t dma_pool_size;
>> +       u64 dma_pool_perms;
>>          struct bam_dmux_skb_dma rx_skbs[BAM_DMUX_NUM_SKB];
>>          struct bam_dmux_skb_dma tx_skbs[BAM_DMUX_NUM_SKB];
>>          spinlock_t tx_lock; /* Protect tx_skbs, tx_next_skb */
>> @@ -762,6 +768,90 @@ static int __maybe_unused bam_dmux_runtime_resume(struct device *dev)
>>          return 0;
>>   }
>>
>> +static int bam_dmux_assign_dma_pool(struct bam_dmux *dmux)
>> +{
>> +       struct device *dev = dmux->dev;
>> +       struct device_node *rmem_np;
>> +       struct reserved_mem *rmem;
>> +       struct qcom_scm_vmperm dst[2];
>> +       u64 src = BIT_ULL(QCOM_SCM_VMID_HLOS);
>> +       u32 vmid;
>> +       int ret;
>> +
>> +       if (!of_property_present(dev->of_node, "qcom,vmid"))
>> +               return 0;
>> +
>> +       ret = of_property_read_u32(dev->of_node, "qcom,vmid", &vmid);
>> +       if (ret)
>> +               return dev_err_probe(dev, ret, "Failed to read qcom,vmid\n");
>> +       if (vmid == QCOM_SCM_VMID_HLOS || vmid >= BITS_PER_TYPE(u64))
>> +               return dev_err_probe(dev, -EINVAL, "Invalid qcom,vmid %u\n", vmid);
>> +
>> +       if (!IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL))
>> +               return dev_err_probe(dev, -EOPNOTSUPP,
>> +                                    "qcom,vmid requires DMA_RESTRICTED_POOL\n");
>> +
>> +       rmem_np = of_parse_phandle(dev->of_node, "memory-region", 0);
>> +       if (!rmem_np)
>> +               return dev_err_probe(dev, -EINVAL,
>> +                                            "qcom,vmid requires memory-region\n");
>> +
>> +       rmem = of_reserved_mem_lookup(rmem_np);
>> +       of_node_put(rmem_np);
>> +       if (!rmem)
>> +               return dev_err_probe(dev, -EINVAL,
>> +                                            "Failed to look up restricted DMA pool\n");
>> +
>> +       if (!is_swiotlb_for_alloc(dev))
>> +               return dev_err_probe(dev, -EINVAL,
>> +                                    "Restricted DMA pool not attached\n");
>> +
>> +       if (!qcom_scm_is_available())
>> +               return -EPROBE_DEFER;
>> +
>> +       dst[0].vmid = QCOM_SCM_VMID_HLOS;
>> +       dst[0].perm = QCOM_SCM_PERM_RW;
>> +       dst[1].vmid = vmid;
>> +       dst[1].perm = QCOM_SCM_PERM_RW;
>> +
>> +       ret = qcom_scm_assign_mem(rmem->base, rmem->size, &src, dst,
>> +                                 ARRAY_SIZE(dst));
>> +       if (ret)
>> +               return dev_err_probe(dev, ret,
>> +                                    "SCM assign restricted DMA pool failed\n");
>> +
>> +       dmux->dma_pool_base = rmem->base;
>> +       dmux->dma_pool_size = rmem->size;
>> +       /* Track the destination VMIDs explicitly for the reclaim operation. */
>> +       dmux->dma_pool_perms = BIT_ULL(QCOM_SCM_VMID_HLOS) | BIT_ULL(vmid);
>> +
>> +       return 0;
>> +}
>> +
>> +static void bam_dmux_reclaim_dma_pool(struct bam_dmux *dmux)
>> +{
>> +       struct qcom_scm_vmperm hlos = {
>> +               .vmid = QCOM_SCM_VMID_HLOS,
>> +               .perm = QCOM_SCM_PERM_RW,
>> +       };
>> +       u64 src = dmux->dma_pool_perms;
>> +       int ret;
>> +
>> +       if (!dmux->dma_pool_perms)
>> +               return;
>> +
>> +       ret = qcom_scm_assign_mem(dmux->dma_pool_base, dmux->dma_pool_size, &src,
>> +                                 &hlos, 1);
>> +       if (ret) {
>> +               dev_err(dmux->dev, "SCM reclaim restricted DMA pool failed: %d\n", ret);
>> +               return;
>> +       }
>> +
>> +       dmux->dma_pool_perms = 0;
>> +}
>> +
>> +static void bam_dmux_remove(struct platform_device *pdev);
>> +
>>   static int bam_dmux_probe(struct platform_device *pdev)
>>   {
>>          struct device *dev = &pdev->dev;
>> @@ -796,6 +886,10 @@ static int bam_dmux_probe(struct platform_device *pdev)
>>                                       "Failed to get pc-ack state\n");
>>          dmux->pc_ack_mask = BIT(bit);
>>
>> +       ret = bam_dmux_assign_dma_pool(dmux);
>> +       if (ret)
>> +               return ret;
>> +
>>          init_waitqueue_head(&dmux->pc_wait);
>>          init_completion(&dmux->pc_ack_completion);
>>          complete_all(&dmux->pc_ack_completion);
>> @@ -829,8 +923,11 @@ static int bam_dmux_probe(struct platform_device *pdev)
>>
>>          ret = irq_get_irqchip_state(dmux->pc_irq, IRQCHIP_STATE_LINE_LEVEL,
>>                                      &dmux->pc_state);
>> -       if (ret)
>> -               goto err_disable_pm;
>> +       if (ret) {
>> +               /* The PC IRQ may already have powered up the RX path */
>> +               bam_dmux_remove(pdev);
> it's still unclear in the comment and commit message why we can't go
> with err_disable_pm?

Agreed. I plan to update the comment in the next revision to:

/*
  * The PC IRQ is already enabled and may have powered up the RX
  * path. Use the full remove() teardown so that RX DMA is stopped
  * before the pool is reclaimed.
  */

and add to the commit message:

If probe fails after the PC IRQ has been requested, clean up through
bam_dmux_remove(), since the IRQ may already have powered up the RX
path, which must be torn down before the pool is reclaimed.

Does this look fine to you?


Vishnu

>
>> +               return ret;
>> +       }
>>
>>          /* Check if remote finished initialization before us */
>>          if (dmux->pc_state) {
>> @@ -845,6 +942,7 @@ static int bam_dmux_probe(struct platform_device *pdev)
>>   err_disable_pm:
>>          pm_runtime_disable(dev);
>>          pm_runtime_dont_use_autosuspend(dev);
>> +       bam_dmux_reclaim_dma_pool(dmux);
>>          return ret;
>>   }
>>
>> @@ -879,6 +977,12 @@ static void bam_dmux_remove(struct platform_device *pdev)
>>          disable_irq(dmux->pc_irq);
>>          bam_dmux_power_off(dmux);
>>          bam_dmux_free_skbs(dmux->tx_skbs, DMA_TO_DEVICE);
>> +
>> +       /* The remote side may still access the pool if it holds its power vote */
>> +       if (!dmux->pc_state)
>> +               bam_dmux_reclaim_dma_pool(dmux);
>> +       else if (dmux->dma_pool_perms)
>> +               dev_warn(dev, "Leaving restricted DMA pool assigned to remote\n");
>>   }
>>
>>   static const struct dev_pm_ops bam_dmux_pm_ops = {
>>
>> --
>> 2.34.1
>>

Re: [PATCH net-next v5 2/2] net: wwan: qcom_bam_dmux: Assign restricted DMA pool to remote processor

[Loic Poulain]

On Fri, Nov 6, 2026 at 5:36 AM Vishnu Santhosh
<vishnu.santhosh@oss.qualcomm.com> wrote:
>
>
> On 05-11-2026 07:51 pm, Loic Poulain wrote:
> > On Thu, Nov 5, 2026 at 11:42 AM Vishnu Santhosh
> > <vishnu.santhosh@oss.qualcomm.com> wrote:
> >> Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
> >> domain with restricted access to system memory. BAM-DMUX DMA mappings
> >> and BAM descriptor FIFOs must therefore be constrained to a designated
> >> memory region that can be shared with the modem. Accesses outside that
> >> region can trigger an XPU violation.
> >>
> >> When qcom,vmid is present, require a restricted DMA pool and assign the
> >> entire pool to both the local and remote execution environments before
> >> requesting the DMA channels.
> >>
> >> This ensures that BAM-DMUX mappings are within the assigned region. When
> >> the BAM DMA controller references the same pool, its descriptor FIFOs
> >> are covered by the assignment as well.
> >>
> >> Track the assigned execution environments explicitly and reclaim the
> >> pool for the local environment after DMA channels and mappings are
> >> released during remove or probe error cleanup. Skip the reclaim and
> >> leave the pool assigned if the remote side still holds its power vote,
> >> since it may still access the pool.
> >>
> >> Fail probing when restricted DMA pool support is unavailable, when the
> >> VMID property is malformed, when memory-region is missing, or when the
> >> restricted DMA pool is not attached to the device.
> >>
> >> Co-developed-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
> >> Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
> >> Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
> >> ---
> >>   drivers/net/wwan/Kconfig         |   1 +
> >>   drivers/net/wwan/qcom_bam_dmux.c | 108 ++++++++++++++++++++++++++++++++++++++-
> >>   2 files changed, 107 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/net/wwan/Kconfig b/drivers/net/wwan/Kconfig
> >> index 958dbc7347fa84ee869439bf8b503037faab8bef..1b133c56231615269698140187ca3141dfe48dbf 100644
> >> --- a/drivers/net/wwan/Kconfig
> >> +++ b/drivers/net/wwan/Kconfig
> >> @@ -65,6 +65,7 @@ config MHI_WWAN_MBIM
> >>   config QCOM_BAM_DMUX
> >>          tristate "Qualcomm BAM-DMUX WWAN network driver"
> >>          depends on (DMA_ENGINE && PM && QCOM_SMEM_STATE) || COMPILE_TEST
> >> +       select QCOM_SCM
> >>          help
> >>            The BAM Data Multiplexer provides access to the network data channels
> >>            of modems integrated into many older Qualcomm SoCs, e.g. Qualcomm
> >> diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
> >> index cc6ace8d64371eb8d00c638a39b234ee540b83c9..0e7ad62f8b4e059264e89837f296ee13c0c31c9b 100644
> >> --- a/drivers/net/wwan/qcom_bam_dmux.c
> >> +++ b/drivers/net/wwan/qcom_bam_dmux.c
> >> @@ -9,14 +9,17 @@
> >>   #include <linux/completion.h>
> >>   #include <linux/dma-mapping.h>
> >>   #include <linux/dmaengine.h>
> >> +#include <linux/firmware/qcom/qcom_scm.h>
> >>   #include <linux/if_arp.h>
> >>   #include <linux/interrupt.h>
> >>   #include <linux/module.h>
> >>   #include <linux/netdevice.h>
> >> +#include <linux/of_reserved_mem.h>
> >>   #include <linux/platform_device.h>
> >>   #include <linux/pm_runtime.h>
> >>   #include <linux/soc/qcom/smem_state.h>
> >>   #include <linux/spinlock.h>
> >> +#include <linux/swiotlb.h>
> >>   #include <linux/wait.h>
> >>   #include <linux/workqueue.h>
> >>   #include <net/pkt_sched.h>
> >> @@ -75,6 +78,9 @@ struct bam_dmux {
> >>          struct completion pc_ack_completion;
> >>
> >>          struct dma_chan *rx, *tx;
> >> +       phys_addr_t dma_pool_base;
> >> +       size_t dma_pool_size;
> >> +       u64 dma_pool_perms;
> >>          struct bam_dmux_skb_dma rx_skbs[BAM_DMUX_NUM_SKB];
> >>          struct bam_dmux_skb_dma tx_skbs[BAM_DMUX_NUM_SKB];
> >>          spinlock_t tx_lock; /* Protect tx_skbs, tx_next_skb */
> >> @@ -762,6 +768,90 @@ static int __maybe_unused bam_dmux_runtime_resume(struct device *dev)
> >>          return 0;
> >>   }
> >>
> >> +static int bam_dmux_assign_dma_pool(struct bam_dmux *dmux)
> >> +{
> >> +       struct device *dev = dmux->dev;
> >> +       struct device_node *rmem_np;
> >> +       struct reserved_mem *rmem;
> >> +       struct qcom_scm_vmperm dst[2];
> >> +       u64 src = BIT_ULL(QCOM_SCM_VMID_HLOS);
> >> +       u32 vmid;
> >> +       int ret;
> >> +
> >> +       if (!of_property_present(dev->of_node, "qcom,vmid"))
> >> +               return 0;
> >> +
> >> +       ret = of_property_read_u32(dev->of_node, "qcom,vmid", &vmid);
> >> +       if (ret)
> >> +               return dev_err_probe(dev, ret, "Failed to read qcom,vmid\n");
> >> +       if (vmid == QCOM_SCM_VMID_HLOS || vmid >= BITS_PER_TYPE(u64))
> >> +               return dev_err_probe(dev, -EINVAL, "Invalid qcom,vmid %u\n", vmid);
> >> +
> >> +       if (!IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL))
> >> +               return dev_err_probe(dev, -EOPNOTSUPP,
> >> +                                    "qcom,vmid requires DMA_RESTRICTED_POOL\n");
> >> +
> >> +       rmem_np = of_parse_phandle(dev->of_node, "memory-region", 0);
> >> +       if (!rmem_np)
> >> +               return dev_err_probe(dev, -EINVAL,
> >> +                                            "qcom,vmid requires memory-region\n");
> >> +
> >> +       rmem = of_reserved_mem_lookup(rmem_np);
> >> +       of_node_put(rmem_np);
> >> +       if (!rmem)
> >> +               return dev_err_probe(dev, -EINVAL,
> >> +                                            "Failed to look up restricted DMA pool\n");
> >> +
> >> +       if (!is_swiotlb_for_alloc(dev))
> >> +               return dev_err_probe(dev, -EINVAL,
> >> +                                    "Restricted DMA pool not attached\n");
> >> +
> >> +       if (!qcom_scm_is_available())
> >> +               return -EPROBE_DEFER;
> >> +
> >> +       dst[0].vmid = QCOM_SCM_VMID_HLOS;
> >> +       dst[0].perm = QCOM_SCM_PERM_RW;
> >> +       dst[1].vmid = vmid;
> >> +       dst[1].perm = QCOM_SCM_PERM_RW;
> >> +
> >> +       ret = qcom_scm_assign_mem(rmem->base, rmem->size, &src, dst,
> >> +                                 ARRAY_SIZE(dst));
> >> +       if (ret)
> >> +               return dev_err_probe(dev, ret,
> >> +                                    "SCM assign restricted DMA pool failed\n");
> >> +
> >> +       dmux->dma_pool_base = rmem->base;
> >> +       dmux->dma_pool_size = rmem->size;
> >> +       /* Track the destination VMIDs explicitly for the reclaim operation. */
> >> +       dmux->dma_pool_perms = BIT_ULL(QCOM_SCM_VMID_HLOS) | BIT_ULL(vmid);
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static void bam_dmux_reclaim_dma_pool(struct bam_dmux *dmux)
> >> +{
> >> +       struct qcom_scm_vmperm hlos = {
> >> +               .vmid = QCOM_SCM_VMID_HLOS,
> >> +               .perm = QCOM_SCM_PERM_RW,
> >> +       };
> >> +       u64 src = dmux->dma_pool_perms;
> >> +       int ret;
> >> +
> >> +       if (!dmux->dma_pool_perms)
> >> +               return;
> >> +
> >> +       ret = qcom_scm_assign_mem(dmux->dma_pool_base, dmux->dma_pool_size, &src,
> >> +                                 &hlos, 1);
> >> +       if (ret) {
> >> +               dev_err(dmux->dev, "SCM reclaim restricted DMA pool failed: %d\n", ret);
> >> +               return;
> >> +       }
> >> +
> >> +       dmux->dma_pool_perms = 0;
> >> +}
> >> +
> >> +static void bam_dmux_remove(struct platform_device *pdev);
> >> +
> >>   static int bam_dmux_probe(struct platform_device *pdev)
> >>   {
> >>          struct device *dev = &pdev->dev;
> >> @@ -796,6 +886,10 @@ static int bam_dmux_probe(struct platform_device *pdev)
> >>                                       "Failed to get pc-ack state\n");
> >>          dmux->pc_ack_mask = BIT(bit);
> >>
> >> +       ret = bam_dmux_assign_dma_pool(dmux);
> >> +       if (ret)
> >> +               return ret;
> >> +
> >>          init_waitqueue_head(&dmux->pc_wait);
> >>          init_completion(&dmux->pc_ack_completion);
> >>          complete_all(&dmux->pc_ack_completion);
> >> @@ -829,8 +923,11 @@ static int bam_dmux_probe(struct platform_device *pdev)
> >>
> >>          ret = irq_get_irqchip_state(dmux->pc_irq, IRQCHIP_STATE_LINE_LEVEL,
> >>                                      &dmux->pc_state);
> >> -       if (ret)
> >> -               goto err_disable_pm;
> >> +       if (ret) {
> >> +               /* The PC IRQ may already have powered up the RX path */
> >> +               bam_dmux_remove(pdev);
> > it's still unclear in the comment and commit message why we can't go
> > with err_disable_pm?
>
> Agreed. I plan to update the comment in the next revision to:
>
> /*
>   * The PC IRQ is already enabled and may have powered up the RX
>   * path. Use the full remove() teardown so that RX DMA is stopped
>   * before the pool is reclaimed.
>   */
>
> and add to the commit message:
>
> If probe fails after the PC IRQ has been requested, clean up through
> bam_dmux_remove(), since the IRQ may already have powered up the RX
> path, which must be torn down before the pool is reclaimed.
>
> Does this look fine to you?

That looks good, yes. Also, could this be avoided by requesting the
IRQ with IRQF_NO_AUTOEN and only enabling it at the end of the probe
sequence?

>
>
> Vishnu
>
> >
> >> +               return ret;
> >> +       }
> >>
> >>          /* Check if remote finished initialization before us */
> >>          if (dmux->pc_state) {
> >> @@ -845,6 +942,7 @@ static int bam_dmux_probe(struct platform_device *pdev)
> >>   err_disable_pm:
> >>          pm_runtime_disable(dev);
> >>          pm_runtime_dont_use_autosuspend(dev);
> >> +       bam_dmux_reclaim_dma_pool(dmux);
> >>          return ret;
> >>   }
> >>
> >> @@ -879,6 +977,12 @@ static void bam_dmux_remove(struct platform_device *pdev)
> >>          disable_irq(dmux->pc_irq);
> >>          bam_dmux_power_off(dmux);
> >>          bam_dmux_free_skbs(dmux->tx_skbs, DMA_TO_DEVICE);
> >> +
> >> +       /* The remote side may still access the pool if it holds its power vote */
> >> +       if (!dmux->pc_state)
> >> +               bam_dmux_reclaim_dma_pool(dmux);
> >> +       else if (dmux->dma_pool_perms)
> >> +               dev_warn(dev, "Leaving restricted DMA pool assigned to remote\n");
> >>   }
> >>
> >>   static const struct dev_pm_ops bam_dmux_pm_ops = {
> >>
> >> --
> >> 2.34.1
> >>