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

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

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.

-- 
Ville Syrjälä
Intel