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* [PATCH v2] drm/vc4: Set DRM DMA device directly from HVS and V3D
@ 2026-09-28 20:16 Daniel Drake
  2026-10-02 12:06 ` Maíra Canal
  0 siblings, 1 reply; 2+ messages in thread
From: Daniel Drake @ 2026-09-28 20:16 UTC (permalink / raw)
  To: Maxime Ripard, Dave Stevenson, Maíra Canal,
	Raspberry Pi Kernel Maintenance, Maarten Lankhorst,
	Thomas Zimmermann, David Airlie, Simona Vetter
  Cc: dri-devel, linux-kernel, Daniel Drake

vc4 uses of_dma_configure() during bind to set the DMA configuration of
the drm device by borrowing the configuration of one of its component
devices.

This violates driver model expectations that IOMMU probing and domain
attachment occur before driver binding - see commit bcb81ac6ae3c ("iommu:
Get DT/ACPI parsing into the proper probe path").

With the introduction of the bcm2712-iommu driver behind the vc4 hvs
device, a warning is triggered:

    vc4-drm gpu: late IOMMU probe at driver bind, something fishy here!

Instead of configuring the virtual aggregate device, adopt the pattern
used by sun4i/sun8i/exynos where candidate DMA-capable hardware components
register themselves as the device to use for DRM allocations via
drm_dev_set_dma_dev(), provided a DMA device has not already been
assigned.

HVS will typically bind first and claim the DMA device. The gen6 36-bit
DMA mask configuration was moved into vc4_hvs_bind() accordingly. For
older generations, vc4's v3d component continues to be available as a
fallback, and the default platform bus 32-bit DMA mask is retained.

Fixes: da8e393e23ef ("drm/vc4: drv: Adopt the dma configuration from the HVS or V3D component")
Signed-off-by: Daniel Drake <dan@reactivated.net>
---
Changes in v2:
- Fix vc4_bo_purge() to also use the selected DMA device for freeing
  allocations
- Link to v1: https://lore.kernel.org/r/20260927-drm-dma-device-2-v1-1-3230afcdc851@reactivated.net
---
 drivers/gpu/drm/vc4/vc4_bo.c  |  3 ++-
 drivers/gpu/drm/vc4/vc4_drv.c | 27 ---------------------------
 drivers/gpu/drm/vc4/vc4_hvs.c | 14 ++++++++++++++
 drivers/gpu/drm/vc4/vc4_v3d.c |  8 ++++++++
 4 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
index 49ea2ed0996b..320c5a0c71ed 100644
--- a/drivers/gpu/drm/vc4/vc4_bo.c
+++ b/drivers/gpu/drm/vc4/vc4_bo.c
@@ -303,7 +303,8 @@ static void vc4_bo_purge(struct drm_gem_object *obj)
 
 	drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
 
-	dma_free_wc(dev->dev, obj->size, bo->base.vaddr, bo->base.dma_addr);
+	dma_free_wc(drm_dev_dma_dev(dev), obj->size, bo->base.vaddr,
+		    bo->base.dma_addr);
 	bo->base.vaddr = NULL;
 	bo->madv = __VC4_MADV_PURGED;
 }
diff --git a/drivers/gpu/drm/vc4/vc4_drv.c b/drivers/gpu/drm/vc4/vc4_drv.c
index 616caf9d9915..62f1a5731e33 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.c
+++ b/drivers/gpu/drm/vc4/vc4_drv.c
@@ -273,16 +273,6 @@ static void vc4_component_unbind_all(void *ptr)
 	component_unbind_all(vc4->dev, &vc4->base);
 }
 
-static const struct of_device_id vc4_dma_range_matches[] = {
-	{ .compatible = "brcm,bcm2711-hvs" },
-	{ .compatible = "brcm,bcm2712-hvs" },
-	{ .compatible = "brcm,bcm2835-hvs" },
-	{ .compatible = "brcm,bcm2835-v3d" },
-	{ .compatible = "brcm,cygnus-v3d" },
-	{ .compatible = "brcm,vc4-v3d" },
-	{}
-};
-
 static int vc4_drm_bind(struct device *dev)
 {
 	struct platform_device *pdev = to_platform_device(dev);
@@ -295,8 +285,6 @@ static int vc4_drm_bind(struct device *dev)
 	enum vc4_gen gen;
 	int ret = 0;
 
-	dev->coherent_dma_mask = DMA_BIT_MASK(32);
-
 	gen = (enum vc4_gen)of_device_get_match_data(dev);
 
 	if (gen > VC4_GEN_4)
@@ -304,21 +292,6 @@ static int vc4_drm_bind(struct device *dev)
 	else
 		driver = &vc4_drm_driver;
 
-	if (gen >= VC4_GEN_6_C)
-		dma_set_mask_and_coherent(dev, DMA_BIT_MASK(36));
-	else
-		dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
-
-	node = of_find_matching_node_and_match(NULL, vc4_dma_range_matches,
-					       NULL);
-	if (node) {
-		ret = of_dma_configure(dev, node, true);
-		of_node_put(node);
-
-		if (ret)
-			return ret;
-	}
-
 	vc4 = devm_drm_dev_alloc(dev, driver, struct vc4_dev, base);
 	if (IS_ERR(vc4))
 		return PTR_ERR(vc4);
diff --git a/drivers/gpu/drm/vc4/vc4_hvs.c b/drivers/gpu/drm/vc4/vc4_hvs.c
index e715147d091c..305770c87dcf 100644
--- a/drivers/gpu/drm/vc4/vc4_hvs.c
+++ b/drivers/gpu/drm/vc4/vc4_hvs.c
@@ -22,6 +22,7 @@
 #include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/component.h>
+#include <linux/dma-mapping.h>
 #include <linux/platform_device.h>
 
 #include <drm/drm_atomic_helper.h>
@@ -1662,6 +1663,19 @@ static int vc4_hvs_bind(struct device *dev, struct device *master, void *data)
 		hvs->regset.nregs = ARRAY_SIZE(vc4_hvs_regs);
 	}
 
+	if (vc4->gen >= VC4_GEN_6_C) {
+		ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(36));
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * Use the HVS as the DRM device's DMA controller for buffer
+	 * allocations if one has not already been configured.
+	 */
+	if (drm_dev_dma_dev(drm) == drm->dev)
+		drm_dev_set_dma_dev(drm, dev);
+
 	if (vc4->gen >= VC4_GEN_5) {
 		struct rpi_firmware *firmware;
 		struct device_node *node;
diff --git a/drivers/gpu/drm/vc4/vc4_v3d.c b/drivers/gpu/drm/vc4/vc4_v3d.c
index f32410420d3e..1f76d4850122 100644
--- a/drivers/gpu/drm/vc4/vc4_v3d.c
+++ b/drivers/gpu/drm/vc4/vc4_v3d.c
@@ -10,6 +10,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 
+#include <drm/drm_drv.h>
 #include <drm/drm_print.h>
 
 #include "vc4_drv.h"
@@ -443,6 +444,13 @@ static int vc4_v3d_bind(struct device *dev, struct device *master, void *data)
 	vc4->v3d = v3d;
 	v3d->vc4 = vc4;
 
+	/*
+	 * In headless setups where HVS is absent, use V3D as the fallback
+	 * DMA controller for buffer allocations.
+	 */
+	if (drm_dev_dma_dev(drm) == drm->dev)
+		drm_dev_set_dma_dev(drm, dev);
+
 	v3d->clk = devm_clk_get_optional(dev, NULL);
 	if (IS_ERR(v3d->clk))
 		return dev_err_probe(dev, PTR_ERR(v3d->clk), "Failed to get V3D clock\n");

---
base-commit: 16130ac7861fbbaef5564463a9f6be230e00fb24
change-id: 20260927-drm-dma-device-2-7cb00af72069

Best regards,
-- 
Daniel Drake <dan@reactivated.net>


^ permalink raw reply	[flat|nested] 2+ messages in thread
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2026-09-28 20:16 [PATCH v2] drm/vc4: Set DRM DMA device directly from HVS and V3D Daniel Drake
2026-10-02 12:06 ` Maíra Canal

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