[PATCH] drm/atomic: don't reset link-status to GOOD without ALLOW_MODESET

[Simon Ser]

On Wednesday, June 3, 2020 1:36 PM, Daniel Vetter <daniel at ffwll.ch> wrote:

> On Wed, Jun 03, 2020 at 02:13:43PM +0300, Ville Syrjälä wrote:
>
> > On Wed, Jun 03, 2020 at 10:45:23AM +0000, Simon Ser wrote:
> >
> > > In update_output_state, the link-status property was reset to GOOD to
> > > ensure legacy drmModeSetCrtc re-trains the link. However this auto-reset
> > > is also performed on an atomic commit without ALLLOW_MODESET. If a
> >
> > I didn't think udate_output_state() was getting called for
> > non-legacy paths. Where is that coming from?
>
> Oops, I'm blind and you're right, there's no bug. We already only
> force-set this for legacy modeset (and fbcon).

Indeed, good catch Ville. set_config is purely a legacy thing.

> That also means that atomic userspace has to handle this, which is maybe
> not so awesome ... So maybe we need to duct-tape over this for atomic too,
> and in that case it should be only done when ALLOW_MODESET is set.
>
> But maybe all the compositors that care will handle this :-/

Not fond of this because we'll basically end up with some drivers
checking for link-status (none do that yet) and some user-space
resetting it to GOOD. It'll break only if user-space doesn't reset and
a driver which checks link-status is used. Driver-specific behaviour
isn't great.