From: Christopher James Halse Rogers <raof@xxxxxxxxxx>
Until recently, on (at least) nouveau, radeon, and amdgpu attempting to scanout of an
imported dma-buf would silently result in the dma-buf sharing being broken.
While the hardware is capable of scanning out of imported dma-bufs (at least in some circumstances),
these drivers do not currently implement it, so attempts to scan out of such buffers will never succeed.
Add a userspace-visible drm capability and associated driver_feature so that userspace can discover
when scanning out of an imported dma-buf can work.
Signed-off-by: Christopher James Halse Rogers <christopher.halse.rogers@xxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_ioctl.c | 3 +++
include/drm/drm_drv.h | 1 +
include/uapi/drm/drm.h | 21 +++++++++++++++++++++
3 files changed, 25 insertions(+)
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index a7c61c23685a..79ccf638668e 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -285,6 +285,9 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
case DRM_CAP_ADDFB2_MODIFIERS:
req->value = dev->mode_config.allow_fb_modifiers;
break;
+ case DRM_CAP_PRIME_SCANOUT:
+ req->value = drm_core_check_feature(dev, DRIVER_PRIME_SCANOUT);
+ break;
default:
return -EINVAL;
}
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 5699f42195fe..32cc0d956d7e 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -53,6 +53,7 @@ struct drm_mode_create_dumb;
#define DRIVER_RENDER 0x8000
#define DRIVER_ATOMIC 0x10000
#define DRIVER_KMS_LEGACY_CONTEXT 0x20000
+#define DRIVER_PRIME_SCANOUT 0x40000
/**
* struct drm_driver - DRM driver structure
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index b2c52843bc70..c57213cdb702 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -647,6 +647,27 @@ struct drm_gem_open {
#define DRM_CAP_CURSOR_HEIGHT 0x9
#define DRM_CAP_ADDFB2_MODIFIERS 0x10
#define DRM_CAP_PAGE_FLIP_TARGET 0x11
+/**
+ * DRM_CAP_PRIME_SCANOUT
+ *
+ * The PRIME_SCANOUT capability returns whether the driver might be capable
+ * of scanning out of an imported PRIME buffer.
+ *
+ * This does not guarantee that any imported buffer can be scanned out, as
+ * there may be specific requirements that a given buffer might not satisfy.
+ *
+ * If this capability is false then imported PRIME buffers will definitely
+ * never be suitable for scanout.
+ *
+ * Note: Prior to the introduction of this capability, bugs in drivers would
+ * allow userspace to attempt to scan out of imported PRIME buffers. This would
+ * work once, but move the buffer into an inconsistent state where rendering from
+ * the exporting GPU would no longer be seen by the importing GPU.
+ *
+ * It is unsafe for driver-agnostic code to attempt to scan out of an imported
+ * PRIME buffer in the absense of this capability.
+ */
+#define DRM_CAP_PRIME_SCANOUT 0x12
/** DRM_IOCTL_GET_CAP ioctl argument type */
struct drm_get_cap {
--
2.11.0
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