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

[Daniel Vetter]

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).

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 :-/
-Daniel

> 
> > driver reads link-status to figure out whether to re-train the link,
> > this could cause an atomic commit failure. User-space doesn't expect
> > such a failure, because commits without ALLOW_MODESET aren't supposed to
> > fail because of link training issues.
> > 
> > Change update_output_state to implicitly reset link-status to GOOD only
> > if ALLOW_MODESET is set. This is the case for legacy drmModeSetCrtc
> > because drm_atomic_state_init sets it (and is used in
> > drm_atomic_helper_set_config, called from drm_mode_setcrtc).
> > 
> > Drivers don't seem to read link-status at the moment -- they seem to
> > rely on user-space performing a modeset instead. So this shouldn't
> > result in any change in behaviour, this should only prevent future
> > failures if drivers start reading link-status.
> > 
> > Signed-off-by: Simon Ser <contact at emersion.fr>
> > Suggested-by: Pekka Paalanen <ppaalanen at gmail.com>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Cc: Manasi Navare <manasi.d.navare at intel.com>
> > ---
> >  drivers/gpu/drm/drm_atomic.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 965173fd0ac2..3d9d9e6f7397 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -1426,7 +1426,8 @@ static int update_output_state(struct drm_atomic_state *state,
> >  				return ret;
> >  
> >  			/* Make sure legacy setCrtc always re-trains */
> > -			new_conn_state->link_status = DRM_LINK_STATUS_GOOD;
> > +			if (state->allow_modeset)
> > +				new_conn_state->link_status = DRM_LINK_STATUS_GOOD;
> >  		}
> >  	}
> >  
> > -- 
> > 2.26.2
> > 
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Ville Syrjälä
> Intel
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch