[PATCH 1/4] drm/prime: Support dedicated DMA device for dma-buf imports

[Thomas Zimmermann]

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.

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.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/drm_drv.c   |  2 ++
 drivers/gpu/drm/drm_prime.c |  2 +-
 include/drm/drm_device.h    | 37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 17fc5dc708f4..f8c3c9f77d22 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -654,6 +654,8 @@ 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 32a8781cfd67..258858f2f8dd 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -1004,7 +1004,7 @@ 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 6ea54a578cda..a24cac4b2077 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -64,6 +64,23 @@ 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.
+	 *
+	 * Devices on USB and other peripheral busses 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 driver has to acquire a reference on the DMA
+	 * device, which will be owned and released automatically by the
+	 * DRM core.
+	 */
+	struct device *dma_dev;
+
 	/**
 	 * @managed:
 	 *
@@ -327,4 +344,24 @@ struct drm_device {
 	struct dentry *debugfs_root;
 };
 
+/**
+ * drm_dev_dma_dev - returns the DMA device for a DRM device
+ * @dev: DRM device
+ *
+ * Returns the DMA device of the given DRM device. This is usually
+ * the same as the DRM device's parent. Devices on some peripheral
+ * busses, such as USB, are incapable of performing DMA by themselves.
+ * Drivers should set struct &drm_device.dma_dev to the bus controller
+ * to make DMA work. Required for PRIME buffer import.
+ *
+ * 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
-- 
2.48.1