Re: [PATCH] drm/connector: demote connector force-probes for non-master clients

On Fri, Apr 02, 2021 at 01:22:12PM +0200, Simon Ser wrote:

Force-probing a connector can be slow and cause flickering. As this affects the global KMS state, let's make it so only the DRM master can force-probe a connector.

Non-master DRM clients won't be able to force-probe a connector anymore. Instead, KMS will perform a regular read-only connector query.

Signed-off-by: Simon Ser contact@emersion.fr Cc: Daniel Vetter daniel@ffwll.ch Cc: Pekka Paalanen ppaalanen@gmail.com

---

drivers/gpu/drm/drm_connector.c | 11 ++++++++--- include/uapi/drm/drm_mode.h | 7 ++++--- 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index 7631f76e7f34..2f70a52a892b 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -20,6 +20,7 @@

• OF THIS SOFTWARE.

*/

+#include <drm/drm_auth.h> #include <drm/drm_connector.h> #include <drm/drm_edid.h> #include <drm/drm_encoder.h> @@ -2374,9 +2375,13 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,

mutex_lock(&dev->mode_config.mutex); if (out_resp->count_modes == 0) {

• connector->funcs->fill_modes(connector,
  

• 			     dev->mode_config.max_width,
  

• 			     dev->mode_config.max_height);
  

• if (drm_is_current_master(file_priv))
  

• 	connector->funcs->fill_modes(connector,
  

• 				     dev->mode_config.max_width,
  

• 				     dev->mode_config.max_height);
  

• else
  

• 	drm_dbg_kms(dev, "User-space requested a forced probe on [CONNECTOR:%d:%s] but is not the DRM master, demoting to read-only probe",
  

• 		    connector->base.id, connector->name);
  

  }

  out_resp->mm_width = connector->display_info.width_mm;

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h index a5e76aa06ad5..3efa2e38d89b 100644 --- a/include/uapi/drm/drm_mode.h +++ b/include/uapi/drm/drm_mode.h @@ -413,9 +413,10 @@ enum drm_mode_subconnector {

• **Force-probing a connector**

• • If the @count_modes field is set to zero, the kernel will perform a forced
• • probe on the connector to refresh the connector status, modes and EDID.
• • A forced-probe can be slow, might cause flickering and the ioctl will block.

• • If the @count_modes field is set to zero and the DRM client is the DRM

*current* DRM master

The drm master/client relationship survives a DROPMASTER ioctl, but also it's only really relevant for the old authmagic dance. But just to be consistent here.

• • master, the kernel will perform a forced probe on the connector to refresh
• • the connector status, modes and EDID. A forced-probe can be slow, might
• • cause flickering and the ioctl will block.

Do we have an igt for this? Timing test should do the job I think, assuming we have at least one output which requires an edid read (so maybe skip the test if a forced probe takes less than 10ms or so).

Patch lgtm, but igt would be really nice here.

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

• User-space needs to force-probe connectors to ensure their metadata is
• up-to-date at startup and after receiving a hot-plug event. User-space

-- 2.31.1