Re: [PATCH 1/2] drm/i915/display_wa: Add helpers to check wa

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

On Thu, Jul 03, 2025 at 12:29:37AM +0300, Ville Syrjälä wrote:
> On Wed, Jul 02, 2025 at 03:25:21PM -0500, Lucas De Marchi wrote:
> > On Wed, Jul 02, 2025 at 10:40:34PM +0300, Ville Syrjälä wrote:
> > >On Wed, Jul 02, 2025 at 02:16:18PM +0530, Ankit Nautiyal wrote:
> > >> Introduce a generic helper to check display workarounds using an enum.
> > >>
> > >> Convert Wa_16023588340 to use the new interface, simplifying WA checks
> > >> and making future additions easier.
> > >>
> > >> v2: Use drm_WARN instead of MISSING_CASE and simplify intel_display_wa
> > >> macro. (Jani)
> > >>
> > >> Suggested-by: Jani Nikula <jani.nikula@intel.com>
> > >> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> > >> ---
> > >>  drivers/gpu/drm/i915/display/intel_display_wa.c | 15 +++++++++++++++
> > >>  drivers/gpu/drm/i915/display/intel_display_wa.h |  9 +++++++++
> > >>  drivers/gpu/drm/i915/display/intel_fbc.c        |  2 +-
> > >>  3 files changed, 25 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/gpu/drm/i915/display/intel_display_wa.c b/drivers/gpu/drm/i915/display/intel_display_wa.c
> > >> index f57280e9d041..f5e8d58d9a68 100644
> > >> --- a/drivers/gpu/drm/i915/display/intel_display_wa.c
> > >> +++ b/drivers/gpu/drm/i915/display/intel_display_wa.c
> > >> @@ -3,6 +3,8 @@
> > >>   * Copyright © 2023 Intel Corporation
> > >>   */
> > >>
> > >> +#include "drm/drm_print.h"
> > >> +
> > >>  #include "i915_reg.h"
> > >>  #include "intel_de.h"
> > >>  #include "intel_display_core.h"
> > >> @@ -39,3 +41,16 @@ void intel_display_wa_apply(struct intel_display *display)
> > >>  	else if (DISPLAY_VER(display) == 11)
> > >>  		gen11_display_wa_apply(display);
> > >>  }
> > >> +
> > >> +bool __intel_display_wa(struct intel_display *display, enum intel_display_wa wa)
> > >> +{
> > >> +	switch (wa) {
> > >> +	case INTEL_DISPLAY_WA_16023588340:
> > >> +		return intel_display_needs_wa_16023588340(display);
> > >> +	default:
> > >> +		drm_WARN(display->drm, 1, "Missing Wa number: %d\n", wa);
> > >> +		break;
> > >> +	}
> > >> +
> > >> +	return false;
> > >> +}
> > >> diff --git a/drivers/gpu/drm/i915/display/intel_display_wa.h b/drivers/gpu/drm/i915/display/intel_display_wa.h
> > >> index babd9d16603d..146ee70d66f7 100644
> > >> --- a/drivers/gpu/drm/i915/display/intel_display_wa.h
> > >> +++ b/drivers/gpu/drm/i915/display/intel_display_wa.h
> > >> @@ -21,4 +21,13 @@ static inline bool intel_display_needs_wa_16023588340(struct intel_display *disp
> > >>  bool intel_display_needs_wa_16023588340(struct intel_display *display);
> > >>  #endif
> > >>
> > >> +enum intel_display_wa {
> > >> +	INTEL_DISPLAY_WA_16023588340,
> > >
> > >How is anyone supposed to keep track of these random numbers
> > >and what they mean?
> > 
> > they mean there's a h/w workaround that requires that and this is the id
> > if you need to find more details about it or what platforms/IPs use
> > that.
> 
> I don't want to go look up all the details in the common case.
> I just want to read the code and see that it generally makes
> sense without having to trawl through the spec/hsd for an
> hour every time.
> 
> > 
> > >
> > >The only time I want to see these numbers is if I really have to
> > >open the spec/hsd for it to double check some details. Othwerwise
> > >it just seems like pointless noise that makes it harder to follow
> > >the code/figure out what the heck is going on.
> > 
> > what is the alternative? The current status quo checking by platform
> > and/or IP version, dissociated from the WA numbers?
> 
> I find it easiest if everything is in one place. I think every
> w/a generally should have these:
> - which hardware is affected
> - what other runtime conditions are required to hit the issue
> - what is being done to avoid the issue
> - a short human readable explanation of the issue
> - the w/a number for looking up futher details
> 
> Splitting it all up into random bits and pieces just means more
> jumping around all the time, which I find annoying at best.

I suppose one could argue for a more formal thing for these three:
- which hardware is affected
- a short human readable explanation of the issue
- the w/a number for looking up futher details

Might be still a real pain to deal with that due to having to jump
around, but at least it could be used to force people to document
each w/a a bit better.

Basically anything that avoids having to wait for the spec/hsd to
load is a good thing in my book.

There's also the question of what to do with duplicates, as in often
it seems the same issue is present on multiple platforms under different
w/a numbers.

-- 
Ville Syrjälä
Intel