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@xxxxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: Pekka Paalanen <ppaalanen@xxxxxxxxx>
> ---
> 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@xxxxxxxx>
> *
> * 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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