drm/prime: Support dedicated DMA device for dma-buf imports

Importing dma-bufs via PRIME requires a DMA-capable device. Devices on
peripheral busses, such as USB, often cannot perform DMA by themselves.
Without DMA-capable device PRIME import fails. DRM drivers for USB
devices already use a separate DMA device for dma-buf imports. Make the
mechanism generally available.

Besides the case of USB, there are embedded DRM devices without DMA
capability. DMA is performed by a separate controller. DRM drivers should
set this accordingly.

Add the field dma_dev to struct drm_device to refer to the device's DMA
device. For USB this should be the USB controller. Use dma_dev in the
PRIME import helpers, if set.

v2:
- acquire internal reference on dma_dev (Jani)
- add DMA-controller usecase to docs (Maxime)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250307080836.42848-2-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 17fc5dc708f472bee06b950a89583c83799eba6d..c9487bc88624c966478f5f4b99867427dbd95949 100644 (file)
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -500,6 +500,25 @@ void drm_dev_unplug(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_dev_unplug);
 
+/**
+ * drm_dev_set_dma_dev - set the DMA device for a DRM device
+ * @dev: DRM device
+ * @dma_dev: DMA device or NULL
+ *
+ * Sets the DMA device of the given DRM device. Only required if
+ * the DMA device is different from the DRM device's parent. After
+ * calling this function, the DRM device holds a reference on
+ * @dma_dev. Pass NULL to clear the DMA device.
+ */
+void drm_dev_set_dma_dev(struct drm_device *dev, struct device *dma_dev)
+{
+       dma_dev = get_device(dma_dev);
+
+       put_device(dev->dma_dev);
+       dev->dma_dev = dma_dev;
+}
+EXPORT_SYMBOL(drm_dev_set_dma_dev);
+
 /*
  * Available recovery methods for wedged device. To be sent along with device
  * wedged uevent.
@@ -654,6 +673,8 @@ static void drm_dev_init_release(struct drm_device *dev, void *res)
 {
        drm_fs_inode_free(dev->anon_inode);
 
+       put_device(dev->dma_dev);
+       dev->dma_dev = NULL;
        put_device(dev->dev);
        /* Prevent use-after-free in drm_managed_release when debugging is
         * enabled. Slightly awkward, but can't really be helped. */

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index a3d64f93a225944a760cd618c362b82031edfb56..4b8c6075e46a26413c0468a1b17af6438d703cef 100644 (file)
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -997,7 +997,7 @@ EXPORT_SYMBOL(drm_gem_prime_import_dev);
 struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
                                            struct dma_buf *dma_buf)
 {
-       return drm_gem_prime_import_dev(dev, dma_buf, dev->dev);
+       return drm_gem_prime_import_dev(dev, dma_buf, drm_dev_dma_dev(dev));
 }
 EXPORT_SYMBOL(drm_gem_prime_import);
 

diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index 6ea54a578cdaab0ac91cb55133451ea7c07d1466..e2f894f1b90a7b86ef5755966334a80b0f44361b 100644 (file)
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -64,6 +64,28 @@ struct drm_device {
        /** @dev: Device structure of bus-device */
        struct device *dev;
 
+       /**
+        * @dma_dev:
+        *
+        * Device for DMA operations. Only required if the device @dev
+        * cannot perform DMA by itself. Should be NULL otherwise. Call
+        * drm_dev_dma_dev() to get the DMA device instead of using this
+        * field directly. Call drm_dev_set_dma_dev() to set this field.
+        *
+        * DRM devices are sometimes bound to virtual devices that cannot
+        * perform DMA by themselves. Drivers should set this field to the
+        * respective DMA controller.
+        *
+        * Devices on USB and other peripheral busses also cannot perform
+        * DMA by themselves. The @dma_dev field should point the bus
+        * controller that does DMA on behalve of such a device. Required
+        * for importing buffers via dma-buf.
+        *
+        * If set, the DRM core automatically releases the reference on the
+        * device.
+        */
+       struct device *dma_dev;
+
        /**
         * @managed:
         *
@@ -327,4 +349,23 @@ struct drm_device {
        struct dentry *debugfs_root;
 };
 
+void drm_dev_set_dma_dev(struct drm_device *dev, struct device *dma_dev);
+
+/**
+ * drm_dev_dma_dev - returns the DMA device for a DRM device
+ * @dev: DRM device
+ *
+ * Returns the DMA device of the given DRM device. By default, this
+ * the DRM device's parent. See drm_dev_set_dma_dev().
+ *
+ * Returns:
+ * A DMA-capable device for the DRM device.
+ */
+static inline struct device *drm_dev_dma_dev(struct drm_device *dev)
+{
+       if (dev->dma_dev)
+               return dev->dma_dev;
+       return dev->dev;
+}
+
 #endif