[PATCH v7 1/3] cdx: add support for bus mastering

[PATCH v7 1/3] cdx: add support for bus mastering

[Nipun Gupta]

Introduce cdx_set_master() and cdx_clear_master() APIs to support
enable and disable of bus mastering. Drivers need to use these APIs to
enable/disable DMAs from the CDX devices.

Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
---

Changes v6->v7:
- None

Changes v5->v6:
- change cdx_clear_master() to int return type

Changes v4->v5:
- No change in this patch, patch 2/3 and patch 3/3 are updated

Changes v3->v4:
- Added user of the Bus master enable and disable APIs in patch 2/2.
  There is no change in this patch.

Changes v2->v3:
- Changed return value from EOPNOTSUPP to -EOPNOTSUPP in
  cdx_set_master()

Changes v1->v2:
- Replace bme with bus_master_enable
- Added check for dev_configure API callback
- remove un-necessary error prints
- changed conditional to if-else
- updated commit message to use 72 columns

 drivers/cdx/cdx.c                       | 32 ++++++++++++++
 drivers/cdx/controller/cdx_controller.c |  4 ++
 drivers/cdx/controller/mcdi_functions.c | 58 +++++++++++++++++++++++++
 drivers/cdx/controller/mcdi_functions.h | 13 ++++++
 include/linux/cdx/cdx_bus.h             | 18 ++++++++
 5 files changed, 125 insertions(+)

diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
index d2cad4c670a0..9efb7584f952 100644
--- a/drivers/cdx/cdx.c
+++ b/drivers/cdx/cdx.c
@@ -182,6 +182,38 @@ cdx_match_id(const struct cdx_device_id *ids, struct cdx_device *dev)
 	return NULL;
 }
 
+int cdx_set_master(struct cdx_device *cdx_dev)
+{
+	struct cdx_controller *cdx = cdx_dev->cdx;
+	struct cdx_device_config dev_config;
+	int ret = -EOPNOTSUPP;
+
+	dev_config.type = CDX_DEV_BUS_MASTER_CONF;
+	dev_config.bus_master_enable = true;
+	if (cdx->ops->dev_configure)
+		ret = cdx->ops->dev_configure(cdx, cdx_dev->bus_num,
+					      cdx_dev->dev_num, &dev_config);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(cdx_set_master);
+
+int cdx_clear_master(struct cdx_device *cdx_dev)
+{
+	struct cdx_controller *cdx = cdx_dev->cdx;
+	struct cdx_device_config dev_config;
+	int ret = -EOPNOTSUPP;
+
+	dev_config.type = CDX_DEV_BUS_MASTER_CONF;
+	dev_config.bus_master_enable = false;
+	if (cdx->ops->dev_configure)
+		ret = cdx->ops->dev_configure(cdx, cdx_dev->bus_num,
+					      cdx_dev->dev_num, &dev_config);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(cdx_clear_master);
+
 /**
  * cdx_bus_match - device to driver matching callback
  * @dev: the cdx device to match against
diff --git a/drivers/cdx/controller/cdx_controller.c b/drivers/cdx/controller/cdx_controller.c
index dc52f95f8978..39aa569d8e07 100644
--- a/drivers/cdx/controller/cdx_controller.c
+++ b/drivers/cdx/controller/cdx_controller.c
@@ -55,6 +55,10 @@ static int cdx_configure_device(struct cdx_controller *cdx,
 	case CDX_DEV_RESET_CONF:
 		ret = cdx_mcdi_reset_device(cdx->priv, bus_num, dev_num);
 		break;
+	case CDX_DEV_BUS_MASTER_CONF:
+		ret = cdx_mcdi_bus_master_enable(cdx->priv, bus_num, dev_num,
+						 dev_config->bus_master_enable);
+		break;
 	default:
 		ret = -EINVAL;
 	}
diff --git a/drivers/cdx/controller/mcdi_functions.c b/drivers/cdx/controller/mcdi_functions.c
index 0158f26533dd..6acd8fea4586 100644
--- a/drivers/cdx/controller/mcdi_functions.c
+++ b/drivers/cdx/controller/mcdi_functions.c
@@ -137,3 +137,61 @@ int cdx_mcdi_reset_device(struct cdx_mcdi *cdx, u8 bus_num, u8 dev_num)
 
 	return ret;
 }
+
+static int cdx_mcdi_ctrl_flag_get(struct cdx_mcdi *cdx, u8 bus_num,
+				  u8 dev_num, u32 *flags)
+{
+	MCDI_DECLARE_BUF(inbuf, MC_CMD_CDX_DEVICE_CONTROL_GET_IN_LEN);
+	MCDI_DECLARE_BUF(outbuf, MC_CMD_CDX_DEVICE_CONTROL_GET_OUT_LEN);
+	size_t outlen;
+	int ret;
+
+	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_GET_IN_BUS, bus_num);
+	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_GET_IN_DEVICE, dev_num);
+	ret = cdx_mcdi_rpc(cdx, MC_CMD_CDX_DEVICE_CONTROL_GET, inbuf,
+			   sizeof(inbuf), outbuf, sizeof(outbuf), &outlen);
+	if (ret)
+		return ret;
+
+	if (outlen != MC_CMD_CDX_DEVICE_CONTROL_GET_OUT_LEN)
+		return -EIO;
+
+	*flags = MCDI_DWORD(outbuf, CDX_DEVICE_CONTROL_GET_OUT_FLAGS);
+
+	return 0;
+}
+
+static int cdx_mcdi_ctrl_flag_set(struct cdx_mcdi *cdx, u8 bus_num,
+				  u8 dev_num, bool enable, int lbn)
+{
+	MCDI_DECLARE_BUF(inbuf, MC_CMD_CDX_DEVICE_CONTROL_SET_IN_LEN);
+	u32 flags;
+	int ret;
+
+	/*
+	 * Get flags and then set/reset BUS_MASTER_BIT according to
+	 * the input params.
+	 */
+	ret = cdx_mcdi_ctrl_flag_get(cdx, bus_num, dev_num, &flags);
+	if (ret)
+		return ret;
+
+	flags = flags & (u32)(~(BIT(lbn)));
+	if (enable)
+		flags |= (1 << lbn);
+
+	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_SET_IN_BUS, bus_num);
+	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_SET_IN_DEVICE, dev_num);
+	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_SET_IN_FLAGS, flags);
+	ret = cdx_mcdi_rpc(cdx, MC_CMD_CDX_DEVICE_CONTROL_SET, inbuf,
+			   sizeof(inbuf), NULL, 0, NULL);
+
+	return ret;
+}
+
+int cdx_mcdi_bus_master_enable(struct cdx_mcdi *cdx, u8 bus_num,
+			       u8 dev_num, bool enable)
+{
+	return cdx_mcdi_ctrl_flag_set(cdx, bus_num, dev_num, enable,
+			MC_CMD_CDX_DEVICE_CONTROL_SET_IN_BUS_MASTER_ENABLE_LBN);
+}
diff --git a/drivers/cdx/controller/mcdi_functions.h b/drivers/cdx/controller/mcdi_functions.h
index 7440ace5539a..a448d6581eb4 100644
--- a/drivers/cdx/controller/mcdi_functions.h
+++ b/drivers/cdx/controller/mcdi_functions.h
@@ -58,4 +58,17 @@ int cdx_mcdi_get_dev_config(struct cdx_mcdi *cdx,
 int cdx_mcdi_reset_device(struct cdx_mcdi *cdx,
 			  u8 bus_num, u8 dev_num);
 
+/**
+ * cdx_mcdi_bus_master_enable - Set/Reset bus mastering for cdx device
+ *				represented by bus_num:dev_num
+ * @cdx: pointer to MCDI interface.
+ * @bus_num: Bus number.
+ * @dev_num: Device number.
+ * @enable: Enable bus mastering if set, disable otherwise.
+ *
+ * Return: 0 on success, <0 on failure
+ */
+int cdx_mcdi_bus_master_enable(struct cdx_mcdi *cdx, u8 bus_num,
+			       u8 dev_num, bool enable);
+
 #endif /* CDX_MCDI_FUNCTIONS_H */
diff --git a/include/linux/cdx/cdx_bus.h b/include/linux/cdx/cdx_bus.h
index bead71b7bc73..8320ec3b9e37 100644
--- a/include/linux/cdx/cdx_bus.h
+++ b/include/linux/cdx/cdx_bus.h
@@ -21,11 +21,13 @@
 struct cdx_controller;
 
 enum {
+	CDX_DEV_BUS_MASTER_CONF,
 	CDX_DEV_RESET_CONF,
 };
 
 struct cdx_device_config {
 	u8 type;
+	bool bus_master_enable;
 };
 
 typedef int (*cdx_scan_cb)(struct cdx_controller *cdx);
@@ -170,4 +172,20 @@ extern struct bus_type cdx_bus_type;
  */
 int cdx_dev_reset(struct device *dev);
 
+/**
+ * cdx_set_master - enables bus-mastering for CDX device
+ * @cdx_dev: the CDX device to enable
+ *
+ * Return: 0 for success, -errno on failure
+ */
+int cdx_set_master(struct cdx_device *cdx_dev);
+
+/**
+ * cdx_clear_master - disables bus-mastering for CDX device
+ * @cdx_dev: the CDX device to disable
+ *
+ * Return: 0 for success, -errno on failure
+ */
+int cdx_clear_master(struct cdx_device *cdx_dev);
+
 #endif /* _CDX_BUS_H_ */
-- 
2.17.1

[PATCH v7 2/3] vfio: add bus master feature to device feature ioctl

[Nipun Gupta]

add bus mastering control to VFIO_DEVICE_FEATURE IOCTL. The VFIO user
can use this feature to enable or disable the Bus Mastering of a
device bound to VFIO.

Co-developed-by: Shubham Rohila <shubham.rohila@amd.com>
Signed-off-by: Shubham Rohila <shubham.rohila@amd.com>
Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
---

Changes v6->v7:
- None

Changes v5->v6:
- Updated description of VFIO_DEVICE_FEATURE_BUS_MASTER IOCTL
- Used 0 for clear and 1 for set bus master operation

Changes in v5:
- This patch is newly added which proposes a new flag
  VFIO_DEVICE_FEATURE_BUS_MASTER in VFIO_DEVICE_FEATURE IOCTL.

 include/uapi/linux/vfio.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 20c804bdc09c..6858cd80d597 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1287,6 +1287,27 @@ struct vfio_device_feature_mig_data_size {
 
 #define VFIO_DEVICE_FEATURE_MIG_DATA_SIZE 9
 
+/**
+ * Upon VFIO_DEVICE_FEATURE_SET, set or clear the BUS mastering for the device
+ * based on the operation specified in op flag.
+ *
+ * The functionality is incorporated for devices that needs bus master control,
+ * but the in-band device interface lacks the support. Consequently, it is not
+ * applicable to PCI devices, as bus master control for PCI devices is managed
+ * in-band through the configuration space. At present, this feature is supported
+ * only for CDX devices.
+ * When the device's BUS MASTER setting is configured as CLEAR, it will result in
+ * blocking all incoming DMA requests from the device. On the other hand, configuring
+ * the device's BUS MASTER setting as SET (enable) will grant the device the
+ * capability to perform DMA to the host memory.
+ */
+struct vfio_device_feature_bus_master {
+	__u32 op;
+#define		VFIO_DEVICE_FEATURE_CLEAR_MASTER	0	/* Clear Bus Master */
+#define		VFIO_DEVICE_FEATURE_SET_MASTER		1	/* Set Bus Master */
+};
+#define VFIO_DEVICE_FEATURE_BUS_MASTER 10
+
 /* -------- API for Type1 VFIO IOMMU -------- */
 
 /**
-- 
2.17.1

[PATCH v7 3/3] vfio-cdx: add bus mastering device feature support

[Nipun Gupta]

Support Bus master enable and disable on VFIO-CDX devices using
VFIO_DEVICE_FEATURE_BUS_MASTER flag over VFIO_DEVICE_FEATURE IOCTL.

Co-developed-by: Shubham Rohila <shubham.rohila@amd.com>
Signed-off-by: Shubham Rohila <shubham.rohila@amd.com>
Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
---

Changes v6->v7:
- Add check for BME in open, thus resulting in correct response
  in feature probe.
- Set vdev_regions to NULL in case of error in vfio device open.

Changes v5->v6:
- Called CDX device reset at cdx_open_device()

Changes v4->v5:
- Use device feature IOCTL instead of adding a new VFIO IOCTL
  for bus master feature.

Changes in v4:
- This patch is newly added which uses cdx_set_master() and
  cdx_clear_master() APIs.

 drivers/vfio/cdx/main.c    | 57 +++++++++++++++++++++++++++++++++++++-
 drivers/vfio/cdx/private.h |  2 ++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/cdx/main.c b/drivers/vfio/cdx/main.c
index c376a69d2db2..53ed8e6c499f 100644
--- a/drivers/vfio/cdx/main.c
+++ b/drivers/vfio/cdx/main.c
@@ -14,7 +14,7 @@ static int vfio_cdx_open_device(struct vfio_device *core_vdev)
 		container_of(core_vdev, struct vfio_cdx_device, vdev);
 	struct cdx_device *cdx_dev = to_cdx_device(core_vdev->dev);
 	int count = cdx_dev->res_count;
-	int i;
+	int i, ret;
 
 	vdev->regions = kcalloc(count, sizeof(struct vfio_cdx_region),
 				GFP_KERNEL_ACCOUNT);
@@ -39,6 +39,17 @@ static int vfio_cdx_open_device(struct vfio_device *core_vdev)
 		if (!(cdx_dev->res[i].flags & IORESOURCE_READONLY))
 			vdev->regions[i].flags |= VFIO_REGION_INFO_FLAG_WRITE;
 	}
+	ret = cdx_dev_reset(core_vdev->dev);
+	if (ret) {
+		kfree(vdev->regions);
+		vdev->regions = NULL;
+		return ret;
+	}
+	ret = cdx_clear_master(cdx_dev);
+	if (ret)
+		vdev->flags &= ~BME_SUPPORT;
+	else
+		vdev->flags |= BME_SUPPORT;
 
 	return 0;
 }
@@ -52,6 +63,49 @@ static void vfio_cdx_close_device(struct vfio_device *core_vdev)
 	cdx_dev_reset(core_vdev->dev);
 }
 
+static int vfio_cdx_bm_ctrl(struct vfio_device *core_vdev, u32 flags,
+			    void __user *arg, size_t argsz)
+{
+	size_t minsz =
+		offsetofend(struct vfio_device_feature_bus_master, op);
+	struct vfio_cdx_device *vdev =
+		container_of(core_vdev, struct vfio_cdx_device, vdev);
+	struct cdx_device *cdx_dev = to_cdx_device(core_vdev->dev);
+	struct vfio_device_feature_bus_master ops;
+	int ret;
+
+	if (!vdev->flags & BME_SUPPORT)
+		return -ENOTTY;
+
+	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_SET,
+				 sizeof(ops));
+	if (ret != 1)
+		return ret;
+
+	if (copy_from_user(&ops, arg, minsz))
+		return -EFAULT;
+
+	switch (ops.op) {
+	case VFIO_DEVICE_FEATURE_CLEAR_MASTER:
+		return cdx_clear_master(cdx_dev);
+	case VFIO_DEVICE_FEATURE_SET_MASTER:
+		return cdx_set_master(cdx_dev);
+	default:
+		return -EINVAL;
+	}
+}
+
+static int vfio_cdx_ioctl_feature(struct vfio_device *device, u32 flags,
+				  void __user *arg, size_t argsz)
+{
+	switch (flags & VFIO_DEVICE_FEATURE_MASK) {
+	case VFIO_DEVICE_FEATURE_BUS_MASTER:
+		return vfio_cdx_bm_ctrl(device, flags, arg, argsz);
+	default:
+		return -ENOTTY;
+	}
+}
+
 static int vfio_cdx_ioctl_get_info(struct vfio_cdx_device *vdev,
 				   struct vfio_device_info __user *arg)
 {
@@ -169,6 +223,7 @@ static const struct vfio_device_ops vfio_cdx_ops = {
 	.open_device	= vfio_cdx_open_device,
 	.close_device	= vfio_cdx_close_device,
 	.ioctl		= vfio_cdx_ioctl,
+	.device_feature = vfio_cdx_ioctl_feature,
 	.mmap		= vfio_cdx_mmap,
 	.bind_iommufd	= vfio_iommufd_physical_bind,
 	.unbind_iommufd	= vfio_iommufd_physical_unbind,
diff --git a/drivers/vfio/cdx/private.h b/drivers/vfio/cdx/private.h
index 8bdc117ea88e..8e9d25913728 100644
--- a/drivers/vfio/cdx/private.h
+++ b/drivers/vfio/cdx/private.h
@@ -23,6 +23,8 @@ struct vfio_cdx_region {
 struct vfio_cdx_device {
 	struct vfio_device	vdev;
 	struct vfio_cdx_region	*regions;
+	u32			flags;
+#define BME_SUPPORT BIT(0)
 };
 
 #endif /* VFIO_CDX_PRIVATE_H */
-- 
2.17.1

Re: [PATCH v7 1/3] cdx: add support for bus mastering

[Alex Williamson]

On Fri, 25 Aug 2023 18:47:14 +0530
Nipun Gupta <nipun.gupta@amd.com> wrote:

> Introduce cdx_set_master() and cdx_clear_master() APIs to support
> enable and disable of bus mastering. Drivers need to use these APIs to
> enable/disable DMAs from the CDX devices.
> 
> Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
> Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
> ---
> 
> Changes v6->v7:
> - None
> 
> Changes v5->v6:
> - change cdx_clear_master() to int return type
> 
> Changes v4->v5:
> - No change in this patch, patch 2/3 and patch 3/3 are updated
> 
> Changes v3->v4:
> - Added user of the Bus master enable and disable APIs in patch 2/2.
>   There is no change in this patch.
> 
> Changes v2->v3:
> - Changed return value from EOPNOTSUPP to -EOPNOTSUPP in
>   cdx_set_master()
> 
> Changes v1->v2:
> - Replace bme with bus_master_enable
> - Added check for dev_configure API callback
> - remove un-necessary error prints
> - changed conditional to if-else
> - updated commit message to use 72 columns
> 
>  drivers/cdx/cdx.c                       | 32 ++++++++++++++
>  drivers/cdx/controller/cdx_controller.c |  4 ++
>  drivers/cdx/controller/mcdi_functions.c | 58 +++++++++++++++++++++++++
>  drivers/cdx/controller/mcdi_functions.h | 13 ++++++
>  include/linux/cdx/cdx_bus.h             | 18 ++++++++
>  5 files changed, 125 insertions(+)
> 
> diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c
> index d2cad4c670a0..9efb7584f952 100644
> --- a/drivers/cdx/cdx.c
> +++ b/drivers/cdx/cdx.c
> @@ -182,6 +182,38 @@ cdx_match_id(const struct cdx_device_id *ids, struct cdx_device *dev)
>  	return NULL;
>  }
>  
> +int cdx_set_master(struct cdx_device *cdx_dev)
> +{
> +	struct cdx_controller *cdx = cdx_dev->cdx;
> +	struct cdx_device_config dev_config;
> +	int ret = -EOPNOTSUPP;
> +
> +	dev_config.type = CDX_DEV_BUS_MASTER_CONF;
> +	dev_config.bus_master_enable = true;
> +	if (cdx->ops->dev_configure)
> +		ret = cdx->ops->dev_configure(cdx, cdx_dev->bus_num,
> +					      cdx_dev->dev_num, &dev_config);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(cdx_set_master);
> +
> +int cdx_clear_master(struct cdx_device *cdx_dev)
> +{
> +	struct cdx_controller *cdx = cdx_dev->cdx;
> +	struct cdx_device_config dev_config;
> +	int ret = -EOPNOTSUPP;
> +
> +	dev_config.type = CDX_DEV_BUS_MASTER_CONF;
> +	dev_config.bus_master_enable = false;
> +	if (cdx->ops->dev_configure)
> +		ret = cdx->ops->dev_configure(cdx, cdx_dev->bus_num,
> +					      cdx_dev->dev_num, &dev_config);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(cdx_clear_master);
> +
>  /**
>   * cdx_bus_match - device to driver matching callback
>   * @dev: the cdx device to match against
> diff --git a/drivers/cdx/controller/cdx_controller.c b/drivers/cdx/controller/cdx_controller.c
> index dc52f95f8978..39aa569d8e07 100644
> --- a/drivers/cdx/controller/cdx_controller.c
> +++ b/drivers/cdx/controller/cdx_controller.c
> @@ -55,6 +55,10 @@ static int cdx_configure_device(struct cdx_controller *cdx,
>  	case CDX_DEV_RESET_CONF:
>  		ret = cdx_mcdi_reset_device(cdx->priv, bus_num, dev_num);
>  		break;
> +	case CDX_DEV_BUS_MASTER_CONF:
> +		ret = cdx_mcdi_bus_master_enable(cdx->priv, bus_num, dev_num,
> +						 dev_config->bus_master_enable);
> +		break;
>  	default:
>  		ret = -EINVAL;
>  	}
> diff --git a/drivers/cdx/controller/mcdi_functions.c b/drivers/cdx/controller/mcdi_functions.c
> index 0158f26533dd..6acd8fea4586 100644
> --- a/drivers/cdx/controller/mcdi_functions.c
> +++ b/drivers/cdx/controller/mcdi_functions.c
> @@ -137,3 +137,61 @@ int cdx_mcdi_reset_device(struct cdx_mcdi *cdx, u8 bus_num, u8 dev_num)
>  
>  	return ret;
>  }
> +
> +static int cdx_mcdi_ctrl_flag_get(struct cdx_mcdi *cdx, u8 bus_num,
> +				  u8 dev_num, u32 *flags)
> +{
> +	MCDI_DECLARE_BUF(inbuf, MC_CMD_CDX_DEVICE_CONTROL_GET_IN_LEN);
> +	MCDI_DECLARE_BUF(outbuf, MC_CMD_CDX_DEVICE_CONTROL_GET_OUT_LEN);
> +	size_t outlen;
> +	int ret;
> +
> +	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_GET_IN_BUS, bus_num);
> +	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_GET_IN_DEVICE, dev_num);
> +	ret = cdx_mcdi_rpc(cdx, MC_CMD_CDX_DEVICE_CONTROL_GET, inbuf,
> +			   sizeof(inbuf), outbuf, sizeof(outbuf), &outlen);
> +	if (ret)
> +		return ret;
> +
> +	if (outlen != MC_CMD_CDX_DEVICE_CONTROL_GET_OUT_LEN)
> +		return -EIO;
> +
> +	*flags = MCDI_DWORD(outbuf, CDX_DEVICE_CONTROL_GET_OUT_FLAGS);
> +
> +	return 0;
> +}
> +
> +static int cdx_mcdi_ctrl_flag_set(struct cdx_mcdi *cdx, u8 bus_num,
> +				  u8 dev_num, bool enable, int lbn)
> +{
> +	MCDI_DECLARE_BUF(inbuf, MC_CMD_CDX_DEVICE_CONTROL_SET_IN_LEN);
> +	u32 flags;
> +	int ret;
> +
> +	/*
> +	 * Get flags and then set/reset BUS_MASTER_BIT according to
> +	 * the input params.
> +	 */

Nit, this function isn't specific to the BUS_MASTER_BIT, but this
comment is.  s/BUS_MASTER_BIT/lbn bit/?  Thanks,

Alex

> +	ret = cdx_mcdi_ctrl_flag_get(cdx, bus_num, dev_num, &flags);
> +	if (ret)
> +		return ret;
> +
> +	flags = flags & (u32)(~(BIT(lbn)));
> +	if (enable)
> +		flags |= (1 << lbn);
> +
> +	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_SET_IN_BUS, bus_num);
> +	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_SET_IN_DEVICE, dev_num);
> +	MCDI_SET_DWORD(inbuf, CDX_DEVICE_CONTROL_SET_IN_FLAGS, flags);
> +	ret = cdx_mcdi_rpc(cdx, MC_CMD_CDX_DEVICE_CONTROL_SET, inbuf,
> +			   sizeof(inbuf), NULL, 0, NULL);
> +
> +	return ret;
> +}
> +
> +int cdx_mcdi_bus_master_enable(struct cdx_mcdi *cdx, u8 bus_num,
> +			       u8 dev_num, bool enable)
> +{
> +	return cdx_mcdi_ctrl_flag_set(cdx, bus_num, dev_num, enable,
> +			MC_CMD_CDX_DEVICE_CONTROL_SET_IN_BUS_MASTER_ENABLE_LBN);
> +}
> diff --git a/drivers/cdx/controller/mcdi_functions.h b/drivers/cdx/controller/mcdi_functions.h
> index 7440ace5539a..a448d6581eb4 100644
> --- a/drivers/cdx/controller/mcdi_functions.h
> +++ b/drivers/cdx/controller/mcdi_functions.h
> @@ -58,4 +58,17 @@ int cdx_mcdi_get_dev_config(struct cdx_mcdi *cdx,
>  int cdx_mcdi_reset_device(struct cdx_mcdi *cdx,
>  			  u8 bus_num, u8 dev_num);
>  
> +/**
> + * cdx_mcdi_bus_master_enable - Set/Reset bus mastering for cdx device
> + *				represented by bus_num:dev_num
> + * @cdx: pointer to MCDI interface.
> + * @bus_num: Bus number.
> + * @dev_num: Device number.
> + * @enable: Enable bus mastering if set, disable otherwise.
> + *
> + * Return: 0 on success, <0 on failure
> + */
> +int cdx_mcdi_bus_master_enable(struct cdx_mcdi *cdx, u8 bus_num,
> +			       u8 dev_num, bool enable);
> +
>  #endif /* CDX_MCDI_FUNCTIONS_H */
> diff --git a/include/linux/cdx/cdx_bus.h b/include/linux/cdx/cdx_bus.h
> index bead71b7bc73..8320ec3b9e37 100644
> --- a/include/linux/cdx/cdx_bus.h
> +++ b/include/linux/cdx/cdx_bus.h
> @@ -21,11 +21,13 @@
>  struct cdx_controller;
>  
>  enum {
> +	CDX_DEV_BUS_MASTER_CONF,
>  	CDX_DEV_RESET_CONF,
>  };
>  
>  struct cdx_device_config {
>  	u8 type;
> +	bool bus_master_enable;
>  };
>  
>  typedef int (*cdx_scan_cb)(struct cdx_controller *cdx);
> @@ -170,4 +172,20 @@ extern struct bus_type cdx_bus_type;
>   */
>  int cdx_dev_reset(struct device *dev);
>  
> +/**
> + * cdx_set_master - enables bus-mastering for CDX device
> + * @cdx_dev: the CDX device to enable
> + *
> + * Return: 0 for success, -errno on failure
> + */
> +int cdx_set_master(struct cdx_device *cdx_dev);
> +
> +/**
> + * cdx_clear_master - disables bus-mastering for CDX device
> + * @cdx_dev: the CDX device to disable
> + *
> + * Return: 0 for success, -errno on failure
> + */
> +int cdx_clear_master(struct cdx_device *cdx_dev);
> +
>  #endif /* _CDX_BUS_H_ */