[Intel-gfx] [PATCH v3 2/4] drm/i915/psr: Prevent PSR exit when a non-pipe related register is written

[Dhinakaran Pandiyan]

On Tue, 2018-04-24 at 14:20 -0700, Rodrigo Vivi wrote:
> On Mon, Apr 23, 2018 at 05:42:40PM -0700, Souza, Jose wrote:
> > On Fri, 2018-04-20 at 15:57 -0700, Rodrigo Vivi wrote:
> > > On Fri, Apr 20, 2018 at 03:27:56PM -0700, José Roberto de Souza
> > > wrote:
> > > > Any write in any display register was causing HW to exit PSR,
> > > > masking it to allow more power savings. Writes to pipe related
> > > > registers will still cause HW to exit PSR.
> > > > This is already masked for PSR2.
> > > 
> > > This seems a good idea indeed with the test case on perspective.
> > 
> > what test cases are thinking? the current ones already do pages flips
> > that will only touch the pipe related registers.
> > 
> > > 
> > > But it needs more tests to make sure it doesn't break
> > > "Display WA #0884: all"
> > 
> > I just tested the WA #0884 and it still causes PSR to exit. I have
> > added a new debugfs that when read it writes to
> > 'I915_WRITE(CURSURFLIVE(pipe), 0);' causing a PSR exit.
> 
> Interesting. Thanks a lot for checking this.
> I guess we are safe then. DK?!
> 

Not sure why it works though, let's give it a try.

It might be worth adding more information about test platform and how
was this was tested in the commit message. Since this is not clearly
documented in bspec, someone is going read this in a few months and
think the code does not make any sense.

Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>


> > 
> > > 
> > > Or we might need to revert that patch before moving with this idea.
> > > 
> > > > 
> > > > Bspec: 7721 and 8042
> > > > 
> > > > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > > > Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> > > > ---
> > > > 
> > > > New patch in this series.
> > > > 
> > > >  drivers/gpu/drm/i915/intel_psr.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_psr.c
> > > > b/drivers/gpu/drm/i915/intel_psr.c
> > > > index 0938df48107a..c907282dc82d 100644
> > > > --- a/drivers/gpu/drm/i915/intel_psr.c
> > > > +++ b/drivers/gpu/drm/i915/intel_psr.c
> > > > @@ -712,7 +712,8 @@ static void hsw_psr_enable_source(struct
> > > > intel_dp *intel_dp,
> > > >  		I915_WRITE(EDP_PSR_DEBUG,
> > > >  			   EDP_PSR_DEBUG_MASK_MEMUP |
> > > >  			   EDP_PSR_DEBUG_MASK_HPD |
> > > > -			   EDP_PSR_DEBUG_MASK_LPSP);
> > > > +			   EDP_PSR_DEBUG_MASK_LPSP |
> > > > +			   EDP_PSR_DEBUG_MASK_DISP_REG_WRITE);
> > > >  	}
> > > >  }
> > > >  
> > > > -- 
> > > > 2.17.0
> > > > 
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