drm: Enable PRIME import/export for all drivers

Call drm_gem_prime_handle_to_fd() and drm_gem_prime_fd_to_handle() by
default if no PRIME import/export helpers have been set. Both functions
are the default for almost all drivers.

DRM drivers implement struct drm_driver.gem_prime_import_sg_table
to import dma-buf objects from other drivers. Having the function
drm_gem_prime_fd_to_handle() functions set by default allows each
driver to import dma-buf objects to itself, even without support for
other drivers.

For drm_gem_prime_handle_to_fd() it is similar: using it by default
allows each driver to export to itself, even without support for other
drivers.

This functionality enables userspace to share per-driver buffers
across process boundaries via PRIME (e.g., wlroots requires this
functionality). The patch generalizes a pattern that has previously
been implemented by GEM VRAM helpers [1] to work with any driver.
For example, gma500 can now run the wlroots-based sway compositor.

v2:
	* clean up docs and TODO comments (Simon, Zack)
	* clean up style in drm_getcap()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/dri-devel/20230302143502.500661-1-contact@emersion.fr/ # 1
Reviewed-by: Simon Ser <contact@emersion.fr>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230620080252.16368-2-tzimmermann@suse.de

2 files changed, 13 insertions, 11 deletions

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 7c9d66ee917d..8e9afe7af19c 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -245,8 +245,7 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
 		req->value = 1;
 		return 0;
 	case DRM_CAP_PRIME:
-		req->value |= dev->driver->prime_fd_to_handle ? DRM_PRIME_CAP_IMPORT : 0;
-		req->value |= dev->driver->prime_handle_to_fd ? DRM_PRIME_CAP_EXPORT : 0;
+		req->value = DRM_PRIME_CAP_IMPORT | DRM_PRIME_CAP_EXPORT;
 		return 0;
 	case DRM_CAP_SYNCOBJ:
 		req->value = drm_core_check_feature(dev, DRIVER_SYNCOBJ);
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index f9d4e228b09e..7b48e0b0284a 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -372,11 +372,12 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
 {
 	struct drm_prime_handle *args = data;
 
-	if (!dev->driver->prime_fd_to_handle)
-		return -ENOSYS;
+	if (dev->driver->prime_fd_to_handle) {
+		return dev->driver->prime_fd_to_handle(dev, file_priv, args->fd,
+						       &args->handle);
+	}
 
-	return dev->driver->prime_fd_to_handle(dev, file_priv,
-			args->fd, &args->handle);
+	return drm_gem_prime_fd_to_handle(dev, file_priv, args->fd, &args->handle);
 }
 
 static struct dma_buf *export_and_register_object(struct drm_device *dev,
@@ -518,15 +519,17 @@ int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
 {
 	struct drm_prime_handle *args = data;
 
-	if (!dev->driver->prime_handle_to_fd)
-		return -ENOSYS;
-
 	/* check flags are valid */
 	if (args->flags & ~(DRM_CLOEXEC | DRM_RDWR))
 		return -EINVAL;
 
-	return dev->driver->prime_handle_to_fd(dev, file_priv,
-			args->handle, args->flags, &args->fd);
+	if (dev->driver->prime_handle_to_fd) {
+		return dev->driver->prime_handle_to_fd(dev, file_priv,
+						       args->handle, args->flags,
+						       &args->fd);
+	}
+	return drm_gem_prime_handle_to_fd(dev, file_priv, args->handle,
+					  args->flags, &args->fd);
 }
 
 /**