[PATCH 1/3] drm: Enable PRIME import/export for all drivers

[Thomas Zimmermann]

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.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Link: https://lore.kernel.org/dri-devel/20230302143502.500661-1-contact@emersion.fr/
---
 drivers/gpu/drm/drm_ioctl.c |  4 ++--
 drivers/gpu/drm/drm_prime.c | 29 ++++++++++++++++++++---------
 include/drm/drm_drv.h       |  6 ++++++
 3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 7c9d66ee917de..faa7018bda0a3 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -245,8 +245,8 @@ 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;
+		req->value |= 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 d29dafce9bb0a..36cecfc7c947b 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -372,11 +372,16 @@ 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;
+	/*
+	 * TODO: Convert remaining drivers to drm_gem_prime_fd_to_handle()
+	 *       and remove this callback.
+	 */
+	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 +523,21 @@ 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);
+	/*
+	 * TODO: Convert remaining drivers to drm_gem_prime_handle_to_fd()
+	 *       and remove this callback.
+	 */
+	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);
 }
 
 /**
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 89e2706cac561..10af1899236a0 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -309,6 +309,9 @@ struct drm_driver {
 	 *
 	 * For an in-depth discussion see :ref:`PRIME buffer sharing
 	 * documentation <prime_buffer_sharing>`.
+	 *
+	 * TODO: Convert remaining drivers to drm_gem_prime_handle_to_fd()
+	 *       and remove this callback.
 	 */
 	int (*prime_handle_to_fd)(struct drm_device *dev, struct drm_file *file_priv,
 				uint32_t handle, uint32_t flags, int *prime_fd);
@@ -320,6 +323,9 @@ struct drm_driver {
 	 *
 	 * For an in-depth discussion see :ref:`PRIME buffer sharing
 	 * documentation <prime_buffer_sharing>`.
+	 *
+	 * TODO: Convert remaining drivers to drm_gem_prime_fd_to_handle()
+	 *       and remove this callback.
 	 */
 	int (*prime_fd_to_handle)(struct drm_device *dev, struct drm_file *file_priv,
 				int prime_fd, uint32_t *handle);
-- 
2.41.0