Re: [Intel-gfx] [PATCH] Revert "drm/i915/dg2: Add preemption changes for Wa_14015141709"

[Matt Atwood <matthew.s.atwood@intel.com>]

On Fri, Aug 26, 2022 at 02:02:33PM -0700, Matt Roper wrote:
> This reverts commit ca6920811aa5428270dd78af0a7a36b10119065a.
> 
> The intent of Wa_14015141709 was to inform us that userspace can no
> longer control object-level preemption as it has on past platforms
> (i.e., by twiddling register bit CS_CHICKEN1[0]).  The description of
> the workaround in the spec wasn't terribly well-written, and when we
> requested clarification from the hardware teams we were told that on the
> kernel side we should also probably stop setting
> FF_SLICE_CS_CHICKEN1[14], which is the register bit that directs the
> hardware to honor the settings in per-context register CS_CHICKEN1.  It
> turns out that this guidance about FF_SLICE_CS_CHICKEN1[14] was a
> mistake; even though CS_CHICKEN1[0] is non-operational and useless to
> userspace, there are other bits in the register that do still work and
> might need to be adjusted by userspace in the future (e.g., to implement
> other workarounds that show up).  If we don't set
> FF_SLICE_CS_CHICKEN1[14] in i915, then those future workarounds would
> not take effect.
> 
> This miscommunication came to light because another workaround
> (Wa_16013994831) has now shown up that requires userspace to adjust the
> value of CS_CHICKEN[10] in certain circumstances.  To ensure userspace's
> updates to this chicken bit are handled properly by the hardware, we
> need to make sure that FF_SLICE_CS_CHICKEN1[14] is once again set by the
> kernel.
> 
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_workarounds.c | 2 +-
>  drivers/gpu/drm/i915/i915_drv.h             | 3 ---
>  2 files changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> index 3cdb8294e13f..69a0c6a74474 100644
> --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> @@ -2389,7 +2389,7 @@ rcs_engine_wa_init(struct intel_engine_cs *engine, struct i915_wa_list *wal)
>  			     FF_DOP_CLOCK_GATE_DISABLE);
>  	}
>  
> -	if (HAS_PERCTX_PREEMPT_CTRL(i915)) {
> +	if (IS_GRAPHICS_VER(i915, 9, 12)) {
>  		/* FtrPerCtxtPreemptionGranularityControl:skl,bxt,kbl,cfl,cnl,icl,tgl */
>  		wa_masked_en(wal,
>  			     GEN7_FF_SLICE_CS_CHICKEN1,
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2b00ef3626db..d6a1ab6f65de 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1352,9 +1352,6 @@ IS_SUBPLATFORM(const struct drm_i915_private *i915,
>  #define HAS_GUC_DEPRIVILEGE(dev_priv) \
>  	(INTEL_INFO(dev_priv)->has_guc_deprivilege)
>  
> -#define HAS_PERCTX_PREEMPT_CTRL(i915) \
> -	((GRAPHICS_VER(i915) >= 9) &&  GRAPHICS_VER_FULL(i915) < IP_VER(12, 55))
> -
>  #define HAS_D12_PLANE_MINIMIZATION(dev_priv) (IS_ROCKETLAKE(dev_priv) || \
>  					      IS_ALDERLAKE_S(dev_priv))
>  
> -- 
> 2.37.2
>