Re: [PATCH v3] drm: document how user-space should use link-status

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I'm not 100% sure the paragraph about not resetting link-status or not using ALLOW_MODESET is accurate. Just like the previous version, this is just an attempt at documenting the current kernel behaviour.

drivers/gpu/drm/drm_connector.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index f2b20fd66319..1df036b3353b 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -994,6 +994,26 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {

•  after modeset, the kernel driver may set this to "BAD" and issue a
  

•  hotplug uevent. Drivers should update this value using
  

•  drm_connector_set_link_status_property().
  

• •  When user-space receives the hotplug uevent and detects a "BAD"
    

• •  link-status, the sink doesn't receive pixels anymore (e.g. the screen
    

• •  becomes completely black). The list of available modes may have
    

• •  changed. User-space is expected to pick a new mode if the current one
    

• •  has disappeared and perform a new modeset with link-status set to
    

• •  "GOOD" to re-enable the connector.
    

• •  If multiple connectors share the same CRTC and one of them gets a "BAD"
    

• •  link-status, the other are unaffected (ie. the sinks still continue to
    

• •  receive pixels).
    

• •  When user-space performs an atomic commit on a connector with a "BAD"
    

• •  link-status without resetting the property to "GOOD", the sink may
    

• •  still not receive pixels. When user-space performs an atomic commit
    

• •  which resets the link-status property to "GOOD" without the
    

• •  ALLOW_MODESET flag set, it might fail because a modeset is required.
    

• •  User-space can only change link-status to "GOOD", changing it to "BAD"
    

• •  is a no-op.  
    

Above reads well and is accurate I think. I think we should add another paragraph about the backwards compatibility hack in SETCRTC ioctl:

"For backwards compatibility with non-atomic userspace the kernel tries to automatically set the link-status back to "GOOD" in the SETCRTC IOCTL. This might fail if the mode is no longer valid, similar to how it might fail if a different screen has been connected in the interim."

With that or similar this has my r-b.

Sounds good to me too. A-b stands.

Thanks, pq