Re: [PATCH 1/2] Revert "drm: hide unregistered connectors from GETCONNECTOR IOCTL"

["Jonas Ådahl" <jadahl@redhat.com>]

On Tue, Oct 18, 2022 at 12:58:53PM +0300, Ville Syrjälä wrote:
> On Tue, Oct 18, 2022 at 11:27:19AM +0200, Jonas Ådahl wrote:
> > On Tue, Oct 18, 2022 at 12:14:09PM +0300, Ville Syrjälä wrote:
> > > On Mon, Oct 17, 2022 at 03:31:57PM +0000, Simon Ser wrote:
> > > > This reverts commit 981f09295687f856d5345e19c7084aca481c1395.
> > > > 
> > > > It turns out this breaks Mutter.
> > > 
> > > A bit more detail would be a good to help future archaeologists.
> > 
> > Perhaps a better explanation is
> > 
> > It turns out this causes logically active but disconnected MST display
> > port connectors to disappear from the drmModeGetResources() list,
> 
> That was the whole point was it not? So I'd drop the
> "it turns out" part.
> 
> > meaning userspace is made to believe the connector is already disabled.
> 
> That wording to me implies its a generic issue affecting all
> userspace when so far it looks like only mutter is affected.

Maybe other userspace was? I only found out by testing drm-next, and
only tried using mutter when bisecting.

> So apparently mutter (for some reason) assumes that the
> connector has somehow magically been disabled by someone
> else if it disappears from the list of resources?

Mutter makes the assumption that connectors it can interact with are the
ones that drmModeGetResources() return - nothing magic about that.


Jonas

> 
> > 
> > When userspace then attempts post a new mode set commit, if that commit
> > uses the same CRTC used to previously drive the disconnected connector,
> > it will fail as that CRTC is logically still tied to the disconnected
> > connector.
> > 
> > This was discovered by a bisecting docking station hot plugging
> > regression using mutter.
> > 
> > 
> > Jonas
> > 
> > > 
> > > > 
> > > > Signed-off-by: Simon Ser <contact@emersion.fr>
> > > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > Cc: Lyude Paul <lyude@redhat.com>
> > > > Cc: Jonas Ådahl <jadahl@redhat.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_mode_config.c | 3 ---
> > > >  1 file changed, 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > > > index 939d621c9ad4..688c8afe0bf1 100644
> > > > --- a/drivers/gpu/drm/drm_mode_config.c
> > > > +++ b/drivers/gpu/drm/drm_mode_config.c
> > > > @@ -151,9 +151,6 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
> > > >  	count = 0;
> > > >  	connector_id = u64_to_user_ptr(card_res->connector_id_ptr);
> > > >  	drm_for_each_connector_iter(connector, &conn_iter) {
> > > > -		if (connector->registration_state != DRM_CONNECTOR_REGISTERED)
> > > > -			continue;
> > > > -
> > > >  		/* only expose writeback connectors if userspace understands them */
> > > >  		if (!file_priv->writeback_connectors &&
> > > >  		    (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK))
> > > > -- 
> > > > 2.38.0
> > > > 
> > > 
> > > -- 
> > > Ville Syrjälä
> > > Intel
> > > 
> 
> -- 
> Ville Syrjälä
> Intel
>