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 <tzimmerm...@suse.de>
---
drivers/gpu/drm/drm_drv.c | 21 +++++++++++++++++++
drivers/gpu/drm/drm_prime.c | 2 +-
include/drm/drm_device.h | 41 +++++++++++++++++++++++++++++++++++++
3 files changed, 63 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 17fc5dc708f4..c9487bc88624 100644
--- 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 bdb51c8f262e..ed4e5f06b79d 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -998,7 +998,7 @@ 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..e2f894f1b90a 100644
--- 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
--
2.48.1
