Re: [PATCH 6/9] drm/i915/display_wa: Add support for Wa_14021768792

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 21 Jul 2025, Ankit Nautiyal <ankit.k.nautiyal@intel.com> wrote:
> Some BMG ultrajoiner configurations require support for Link M/N ratios
> between 10.0 and 15.0. This range is not natively supported and requires
> a workaround.
>
> Wa_14021768792 enables this support by utilizing HDMI_EMP_DATA,
> CHICKEN_BITs, and extended bits in the LINK_N registers.
>
> Add the necessary logic to enable the workaround on applicable platforms.
>
> Bspec: 49266
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  .../gpu/drm/i915/display/intel_display_wa.c    | 18 ++++++++++++++++++
>  .../gpu/drm/i915/display/intel_display_wa.h    |  1 +
>  2 files changed, 19 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_wa.c b/drivers/gpu/drm/i915/display/intel_display_wa.c
> index 399c08902413..541967168e97 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_wa.c
> +++ b/drivers/gpu/drm/i915/display/intel_display_wa.c
> @@ -5,11 +5,13 @@
>  
>  #include <drm/drm_print.h>
>  
> +#include "i915_drv.h"

Please do not add new includes of i915_drv.h in display/.

>  #include "i915_reg.h"
>  #include "intel_de.h"
>  #include "intel_display_core.h"
>  #include "intel_display_regs.h"
>  #include "intel_display_wa.h"
> +#include "intel_step.h"
>  
>  static void gen11_display_wa_apply(struct intel_display *display)
>  {
> @@ -52,6 +54,20 @@ static bool intel_display_needs_wa_16025573575(struct intel_display *display)
>  	return DISPLAY_VERx100(display) == 3000 || DISPLAY_VERx100(display) == 3002;
>  }
>  
> +/*
> + * Wa_14021768792:
> + * Fixes: Limitation of Link M/N ratio > 10 for specific Xe2HPD platforms.
> + * Workaround: Use HDMI_EMP_DATA, CHICKEN_BITs and extended bits in LINK_N registers to support
> + * LINK M/N ratios from > 10 but < 15.
> + */
> +static bool intel_display_needs_wa_14021768792(struct intel_display *display)
> +{
> +	struct drm_i915_private *i915 = to_i915(display->drm);

Please do not add new uses of struct drm_i915_private under display/.

> +
> +	return (DISPLAY_VER(display) == 14 && IS_DGFX(i915) &&

s/IS_DGFX(i915)/display->platform.dgfx/

> +		IS_DISPLAY_STEP(display, STEP_C0, STEP_FOREVER));
> +}
> +
>  bool __intel_display_wa(struct intel_display *display, enum intel_display_wa wa, const char *name)
>  {
>  	switch (wa) {
> @@ -59,6 +75,8 @@ bool __intel_display_wa(struct intel_display *display, enum intel_display_wa wa,
>  		return intel_display_needs_wa_16023588340(display);
>  	case INTEL_DISPLAY_WA_16025573575:
>  		return intel_display_needs_wa_16025573575(display);
> +	case INTEL_DISPLAY_WA_14021768792:
> +		return intel_display_needs_wa_14021768792(display);
>  	default:
>  		drm_WARN(display->drm, 1, "Missing Wa number: %s\n", name);
>  		break;
> diff --git a/drivers/gpu/drm/i915/display/intel_display_wa.h b/drivers/gpu/drm/i915/display/intel_display_wa.h
> index aedea4cfa3ce..8470f4ceea1a 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_wa.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_wa.h
> @@ -24,6 +24,7 @@ bool intel_display_needs_wa_16023588340(struct intel_display *display);
>  enum intel_display_wa {
>  	INTEL_DISPLAY_WA_16023588340,
>  	INTEL_DISPLAY_WA_16025573575,
> +	INTEL_DISPLAY_WA_14021768792,
>  };
>  
>  bool __intel_display_wa(struct intel_display *display, enum intel_display_wa wa, const char *name);

-- 
Jani Nikula, Intel