Re: [PATCH 1/2] drm/i915: Don't use DRM_DEBUG_WARN_ON for unexpected l3bank/mslice config

[Matt Roper <matthew.d.roper@intel.com>]

On Wed, May 04, 2022 at 01:07:14PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> DRM_DEBUG_WARN_ON should only be used when we are certain CI is guaranteed
> to exercise a certain code path, so in case of values coming from MMIO
> reads we cannot be sure CI will have all the possible SKUs and parts.
> 
> Use drm_warn instead and move logging to init phase while at it.

Changing to drm_warn looks good, although moving the location changes
the intent a bit; I think originally the idea was to warn if we were
trying to do a steering lookup for a type that we never initialized
(e.g., an LNCF lookup for a !HAS_MSLICES platform where we never even
read the register in the first place).  But I don't think we've ever
made a mistake that would cause us to trip the warning, so it probably
isn't terribly important to keep it there.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>

> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_gt.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
> index 53307ca0eed0..c474e5c3ea5e 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c
> @@ -153,11 +153,14 @@ int intel_gt_init_mmio(struct intel_gt *gt)
>  	 * An mslice is unavailable only if both the meml3 for the slice is
>  	 * disabled *and* all of the DSS in the slice (quadrant) are disabled.
>  	 */
> -	if (HAS_MSLICES(i915))
> +	if (HAS_MSLICES(i915)) {
>  		gt->info.mslice_mask =
>  			slicemask(gt, GEN_DSS_PER_MSLICE) |
>  			(intel_uncore_read(gt->uncore, GEN10_MIRROR_FUSE3) &
>  			 GEN12_MEML3_EN_MASK);
> +		if (!gt->info.mslice_mask) /* should be impossible! */
> +			drm_warn(&i915->drm, "mslice mask all zero!\n");
> +	}
>  
>  	if (IS_DG2(i915)) {
>  		gt->steering_table[MSLICE] = xehpsdv_mslice_steering_table;
> @@ -171,6 +174,8 @@ int intel_gt_init_mmio(struct intel_gt *gt)
>  		gt->info.l3bank_mask =
>  			~intel_uncore_read(gt->uncore, GEN10_MIRROR_FUSE3) &
>  			GEN10_L3BANK_MASK;
> +		if (!gt->info.l3bank_mask) /* should be impossible! */
> +			drm_warn(&i915->drm, "L3 bank mask is all zero!\n");
>  	} else if (HAS_MSLICES(i915)) {
>  		MISSING_CASE(INTEL_INFO(i915)->platform);
>  	}
> @@ -882,20 +887,14 @@ static void intel_gt_get_valid_steering(struct intel_gt *gt,
>  {
>  	switch (type) {
>  	case L3BANK:
> -		GEM_DEBUG_WARN_ON(!gt->info.l3bank_mask); /* should be impossible! */
> -
>  		*sliceid = 0;		/* unused */
>  		*subsliceid = __ffs(gt->info.l3bank_mask);
>  		break;
>  	case MSLICE:
> -		GEM_DEBUG_WARN_ON(!gt->info.mslice_mask); /* should be impossible! */
> -
>  		*sliceid = __ffs(gt->info.mslice_mask);
>  		*subsliceid = 0;	/* unused */
>  		break;
>  	case LNCF:
> -		GEM_DEBUG_WARN_ON(!gt->info.mslice_mask); /* should be impossible! */
> -
>  		/*
>  		 * An LNCF is always present if its mslice is present, so we
>  		 * can safely just steer to LNCF 0 in all cases.
> -- 
> 2.32.0
> 

-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
(916) 356-2795