[Intel-gfx] [RFC 2/2] drm/i915/display: Protect pipe_update against dc3co exit

[Anshuman Gupta]

On 2020-11-30 at 17:28:32 +0200, Imre Deak wrote:
> On Mon, Nov 30, 2020 at 02:46:46PM +0530, Anshuman Gupta wrote:
> > At usual case DC3CO exit happen automatically by DMC f/w whenever
> > PSR2 clears idle. This happens smoothly by DMC f/w to work with flips.
> > But there are certain scenario where DC3CO  Disallowed by driver
> > asynchronous with flips. In such scenario display engine could
> > be already in DC3CO state and driver has disallowed it,
> > It initiates DC3CO exit sequence in DMC f/w which requires a
> > dc3co exit delay of 200us in driver.
> > It requires to protect intel_pipe_update_{update_end} with
> > dc3co exit delay.
> > 
> > Cc: Imre Deak <imre.deak at intel.com>
> > Cc: <stable at vger.kernel.org>
> > Signed-off-by: Anshuman Gupta <anshuman.gupta at intel.com>
> 
> To make sure that it doesn't hide the root cause (or affects unrelated
> platforms), I'd only add locking around DC3co changes with a new lock,
> using lock/unlock helpers in intel_display_power.c called from
> intel_pipe_update_start/end.
> 
> Also please submit this patch separately, w/o the optimization in patch
> 1/2, so we know that this change fixes the problem.
Thanks imre for review comments, i will send a new patch with review comments fixed.
Anshuman Gupta. 
> 
> --Imre
> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_display.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > index ba26545392bc..3b81b98c0daf 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -15924,6 +15924,8 @@ static void intel_update_crtc(struct intel_atomic_state *state,
> >  	else
> >  		intel_fbc_enable(state, crtc);
> >  
> > +	/* Protect intel_pipe_update_{start,end} with power_domians lock */
> > +	mutex_lock(&dev_priv->power_domains.lock);
> >  	/* Perform vblank evasion around commit operation */
> >  	intel_pipe_update_start(new_crtc_state);
> >  
> > @@ -15935,6 +15937,7 @@ static void intel_update_crtc(struct intel_atomic_state *state,
> >  		i9xx_update_planes_on_crtc(state, crtc);
> >  
> >  	intel_pipe_update_end(new_crtc_state);
> > +	mutex_unlock(&dev_prive->power_domains.lock);
> >  
> >  	/*
> >  	 * We usually enable FIFO underrun interrupts as part of the
> > -- 
> > 2.26.2
> >