[Intel-gfx] [PATCH v2] drm/i915: Use crtc_state->has_psr instead of CAN_PSR for pipe update

[Tarun Vyas]

On Mon, Jul 09, 2018 at 11:58:52AM -0700, Dhinakaran Pandiyan wrote:
> On Mon, 2018-07-09 at 11:16 -0700, Tarun Vyas wrote:
> > On Mon, Jul 09, 2018 at 11:30:00AM -0700, Dhinakaran Pandiyan wrote:
> > > 
> > > On Sun, 2018-07-08 at 18:46 -0700, Tarun Vyas wrote:
> > > > 
> > > > In commit "drm/i915: Wait for PSR exit before checking for vblank
> > > > evasion", the idea was to limit the PSR IDLE checks when PSR is
> > > > actually supported. While CAN_PSR does do that check, it doesn't
> > > > applies on a per-crtc basis. crtc_state->has_psr is a more
> > > > granular
> > > > check that avoids everything but pipe A, for the PSR IDLE check.
> > > > 
> > > > With this, the PSR IDLE check should be a *no-op* for all but
> > > > pipe A
> > > > which is what was intended originally.
> > > > 
> > > So, the problem is when we update a non-PSR pipe (B or C) and PSR
> > > is
> > > active on another pipe(A, specifically), we end up waiting for the
> > > pipe
> > > A MMIO to become idle.
> > > 
> > > Can you please update the commit message as the commit message
> > > makes
> > > the per-pipe check sound like an optimization? 
> > > 
> > > This also points to a gap in our testing, I don't see a two pipe
> > > PSR
> > > related IGT.
> > > 
> > That's right. On my KBL chromebook that's running the drm-tip, when I
> > plug-in an external display, so pipe B,
> > I see "[drm:intel_pipe_update_start] *ERROR* PSR idle timed out,
> > atomic update may fail on pipe B", Iadded the pipe
> > name in the DRM_ERROR, may be I should make that change in the v3 of
> > this patch along with updating the commit message.
> > 
> > But, yea, this proves that with the CAN_PSR check, the non-PSR pipes
> > (B/C) wait on pipe-A to exit PSR which doesn't have
> > any reason to do so at that moment, hence the error.
> > 
> > I'll make the commit message changes and add the pipe name in the
> > DRM_ERROR as well ?
> 
> I am thinking you could pass crtc_state to intel_psr_wait_for_idle()
> and then check inside the implementation if the argument is the same as
> the pipe PSR was enabled on and then wait.
> 
> intel_psr_wait_for_idle(crtc_state) {
> 	if (!CAN_PSR() || !crtc_state->has_psr)
> 		return;
> 	...
> }
Hmm, but the CAN_PSR check is already taken care of by intel_psr_compute_config() which then sets has_psr, so just
	if (!crtc_state->has_psr)
		return;
should suffice, right ?

But then, we incur a function call for non-PSR pipes, which will return right away.
> 
> I don't like how intel_psr_wait_for_idle() doesn't care which pipe
> (transcoder actually) MMIO it should wait on.
> 		
> 
> > > 
> > > > 
> > > > Fixes: a608987970b9 ("drm/i915: Wait for PSR exit before checking
> > > > for
> > > > vblank evasion")
> > > > 
> > > > v2: Remove unnecessary parantheses, make checkpatch happy.
> > > > 
> > > > Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > > Signed-off-by: Tarun Vyas <tarun.vyas at intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_sprite.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_sprite.c
> > > > b/drivers/gpu/drm/i915/intel_sprite.c
> > > > index 4990d6e84ddf..83880e3a5f3d 100644
> > > > --- a/drivers/gpu/drm/i915/intel_sprite.c
> > > > +++ b/drivers/gpu/drm/i915/intel_sprite.c
> > > > @@ -118,7 +118,7 @@ void intel_pipe_update_start(const struct
> > > > intel_crtc_state *new_crtc_state)
> > > >  	 * VBL interrupts will start the PSR exit and prevent a
> > > > PSR
> > > >  	 * re-entry as well.
> > > >  	 */
> > > > -	if (CAN_PSR(dev_priv) &&
> > > > intel_psr_wait_for_idle(dev_priv))
> > > > +	if (new_crtc_state->has_psr &&
> > > > intel_psr_wait_for_idle(dev_priv))
> > > >  		DRM_ERROR("PSR idle timed out, atomic update may
> > > > fail\n");
> > > >  
> > > >  	local_irq_disable();
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