[Intel-gfx] [PATCH] drm/i915: WARN if not all pipes are in bigjoiner mask, when copying plane state

[Lisovskiy, Stanislav]

On Wed, May 10, 2023 at 04:47:57PM +0300, Ville Syrjälä wrote:
> On Tue, May 09, 2023 at 02:14:41PM +0300, Stanislav Lisovskiy wrote:
> > There is a suspicion that we might not have all bigjoiner pipes
> > set in correspodent mask, which leads to that not all crtc are added to the state,
> > however because we are copying for instance crtc reference from master crtc
> > to slave crtc, we might be trying to get it via intel_atomic_get_new_crtc_state,
> > which might the return NULL.
> > This is surely not a fix, but at least the WARN should give us some clue and
> > "red light" when this happens.
> > In future we might need to evaluate the logic of adding crtc to the state,
> > to make sure that we always have all affected crtcs in the state,
> > even though such functions already exist, there seem to be still some
> > glitches in this logic.
> > 
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_atomic_plane.c | 13 +++++++++++++
> >  drivers/gpu/drm/i915/display/intel_display.c      |  2 +-
> >  drivers/gpu/drm/i915/display/intel_display.h      |  1 +
> >  3 files changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > index 4125ee07a271..03cbd755261b 100644
> > --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> > @@ -695,6 +695,19 @@ int intel_plane_atomic_check(struct intel_atomic_state *state,
> >  
> >  		new_master_plane_state =
> >  			intel_atomic_get_new_plane_state(state, master_plane);
> > +
> > +		/*
> > +		 * We would be copying plane state from master crtc
> > +		 * however if crtc_state->bigjoiner_pipes doesn't contain both
> > +		 * master and slave, that means that quite likely we didn't call
> > +		 * intel_atomic_get_crtc_state for both, which can cause issues,
> > +		 * like intel_atomic_get_new_crtc_state returning NULL suddently,
> > +		 * when we for example try to use hw.crtc from that plane state.
> > +		 * This WARN might sched some light on out existing issues, also
> > +		 * prevent others from happening in future.
> > +		 */
> > +		drm_WARN_ON(state->base.dev, intel_bigjoiner_num_pipes(new_crtc_state) < 2);
> 
> What you are doing here is basically just
>  if (bigjoiner_pipes)
>   	assert(bigjoiner_pipes != 1);
> which is not going to catch anything.
> 
> We can trivially see that it will never happen given
> how bigjoiner_pipes is initialized.

intel_bigjoiner_num_pipes counts how many pipe are used, 
as I understand in case of bigjoiner we should always have it 
returning 2, right?

For example intel_bigjoiner_adjust_timings uses it currently
same way in our code, also I think there other places:

static void intel_bigjoiner_adjust_timings(const struct intel_crtc_state *crtc_state,
					   struct drm_display_mode *mode)
{
	int num_pipes = intel_bigjoiner_num_pipes(crtc_state);

	if (num_pipes < 2)
		return;

...

I was just willing to check if, we might have this mask
messed up somehow, because we add crtcs to the state based
on this mask. 

However I already checked, problem seems to be
somewhere else. 

Stan

> 
> -- 
> Ville Syrjälä
> Intel