Re: [PATCH v2] drm/i915/fbc: update the impacted platforms in wa_22014263786

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Oct 01, 2025 at 01:20:20PM +0000, Govindapillai, Vinod wrote:
> + I had Lucas' email id wrong. Fixed.
> 
> On Wed, 2025-10-01 at 16:10 +0300, Jani Nikula wrote:
> > On Wed, 01 Oct 2025, "Govindapillai, Vinod" <vinod.govindapillai@intel.com> wrote:
> > > On Wed, 2025-10-01 at 13:03 +0300, Jani Nikula wrote:
> > > > On Wed, 01 Oct 2025, Vinod Govindapillai <vinod.govindapillai@intel.com> wrote:
> > > > > wa_22014263786 is not applicable to the BMG and hence exclude it
> > > > > from the wa.
> > > > > 
> > > > > v2: Limit this wa to display verion 11 to 14, drop DG2 from the
> > > > >     exclusion list, use intel_display_wa (Lucas)
> > > > > 
> > > > > Bspec: 74212, 66624
> > > > > Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/display/intel_display_wa.c | 12 ++++++++++++
> > > > >  drivers/gpu/drm/i915/display/intel_display_wa.h |  1 +
> > > > >  drivers/gpu/drm/i915/display/intel_fbc.c        |  3 +--
> > > > >  3 files changed, 14 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_display_wa.c
> > > > > b/drivers/gpu/drm/i915/display/intel_display_wa.c
> > > > > index 31cd2c9cd488..7ca238725e30 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_display_wa.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_display_wa.c
> > > > > @@ -52,6 +52,16 @@ static bool intel_display_needs_wa_16025573575(struct intel_display
> > > > > *display)
> > > > >  	return DISPLAY_VERx100(display) == 3000 || DISPLAY_VERx100(display) == 3002;
> > > > >  }
> > > > >  
> > > > > +/*
> > > > > + * Wa_22014263786:
> > > > > + * Fixes: Screen flicker with FBC and Package C state enabled
> > > > > + * Workaround: Forced SLB invalidation before start of new frame.
> > > > > + */
> > > > > +static bool intel_display_needs_wa_22014263786(struct intel_display *display)
> > > > > +{
> > > > > +	return DISPLAY_VERx100(display) >= 1100 && DISPLAY_VERx100(display) < 1401;
> > > > 
> > > > IS_DISPLAY_VERx100(display, 1100, 1400)
> > > > 
> > > > Also I'm not sure if we really need separate functions for one-liners
> > > > like this. The documentation could be in the switch case too? *shrug*.
> > > 
> > > Thanks. I will update that. I will get rid of the comments. I dont think it adds any extra
> > > information other than what it can be found from wa details.
> > 
> > But I did not say we should get rid of the comments! We don't want to
> > make people look up the wa details, because it's not publicly available
> > information.
> > 
> > I'm just wondering if we need the separate *function*.
> 
> I got that part. I thought I will remove the comments along with that change! Originally this wa
> also did not have much information as comments other than the impacted platforms. 
> 
> Okay. Will wait for Ville's feedback before floating another version

I think production w/a should generally be included in the public PRMs.
But I don't enjoy looking them up in either internal or public source.

What I would like to see described is the symptoms that are getting
fixed, and whther those symptoms occur under specific circumstancs
(esp. if we decided to apply the w/a as a bigger hammer without
actually checking for those specific circumstances). That sort of
information can be very useful when you're seeing some problem and
pondering whether you might be missing some existing w/a.

Very low level details aren't probably particularly useful even to
us. To really understand those you probably have to trawl the hsd(s)
anyway.

So after some pondering I'm thinking the explanations should perhaps
still stay where the w/a is implemented, and this w/a list would
_only_ contain the platform checks. And I would also want to be able
to immediately jump from the actual code to the relevant w/a platform
check (as in with cscope/etc). Though that's still a somewhat annoying
extra step or two, esp. since I can't directly jump to the defition of
the enum value but rather need to jump to one of its uses in
__intel_displa_wa() :/ I suppose if all of these were functions without
the enum step in the middle that problem would be solved. But dunno if
we want to have a function per w/a number?

-- 
Ville Syrjälä
Intel