On Thu, Aug 24, 2023 at 04:50:20PM -0400, Gil Dekel wrote:
> Before sending a uevent to userspace in order to trigger a corrective
> modeset, we change the failing connector's link-status to BAD. However,
> the downstream MST branch ports are left in their original GOOD state.
>
> This patch utilizes the drm helper function
> drm_dp_set_mst_topology_link_status() to rectify this and set all
> downstream MST connectors' link-status to BAD before emitting the uevent
> to userspace.
>
> Signed-off-by: Gil Dekel <gildekel@xxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 42353b1ac487..e8b10f59e141 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5995,16 +5995,20 @@ static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
> struct intel_dp *intel_dp =
> container_of(work, typeof(*intel_dp), modeset_retry_work);
> struct drm_connector *connector = &intel_dp->attached_connector->base;
> - drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s]\n", connector->base.id,
> - connector->name);
>
> - /* Grab the locks before changing connector property*/
> - mutex_lock(&connector->dev->mode_config.mutex);
> - /* Set connector link status to BAD and send a Uevent to notify
> - * userspace to do a modeset.
> + /* Set the connector's (and possibly all its downstream MST ports') link
> + * status to BAD.
> */
> + mutex_lock(&connector->dev->mode_config.mutex);
> + drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] link status %d -> %d\n",
> + connector->base.id, connector->name,
> + connector->state->link_status, DRM_MODE_LINK_STATUS_BAD);
> drm_connector_set_link_status_property(connector,
> DRM_MODE_LINK_STATUS_BAD);
> + if (intel_dp->is_mst) {
> + drm_dp_set_mst_topology_link_status(&intel_dp->mst_mgr,
> + DRM_MODE_LINK_STATUS_BAD);
Something is weird with the locking here.
I noticed that on patch 3 this new function also gets the same
mutex_lock(&connector->dev->mode_config.mutex);
Since you didn't reach the deadlock, I'm clearly missing something
on the flow. But regardless of what I could be missing, I believe
this is totally not future proof and we will for sure hit dead-lock
cases.
> + }
> mutex_unlock(&connector->dev->mode_config.mutex);
> /* Send Hotplug uevent so userspace can reprobe */
> drm_kms_helper_connector_hotplug_event(connector);
> --
> Gil Dekel, Software Engineer, Google / ChromeOS Display and Graphics
