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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/05/2022 19:17, Matt Roper wrote:
> On Wed, May 04, 2022 at 06:59:32PM +0100, Tvrtko Ursulin wrote:
>>
>> On 04/05/2022 17:48, Matt Roper wrote:
>>> 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.
>>
>> Ah I see.. there we could put something like:
>>
>> 	case MSLICE:
>> 		GEM_WARN_ON(!HAS_MSLICES(...));
>>
> 
> Yeah, that would work for MSLICE and LNCF.  Although L3BANK is a bit
> stranger since we have multiple platforms that obtain the L3 bank mask
> in completely different ways (Xe_HP reads it from XEHP_FUSE4, whereas
> gen11/gen12 reads it from GEN10_MIRROR_FUSE3).  We want to make sure
> there that no matter which branch of init we take, we didn't forget to
> initialize l3bank_mask somehow.

The two init paths are not something present in drm-tip at this point, 
right? At least I couldn't find it. In which case it could be handled 
later by moving the drm_warn to tail of intel_gt_init_mmio, give or take.

Anyway, I've sent v2 out with your r-b and GEM_WARN_ON for mslice/lncf. 
I won't merge it though until you definitely are okay with it so please 
have a look and confirm.

Regards,

Tvrtko


> 
> Matt
> 
>> ?
>>
>> Regards,
>>
>> Tvrtko
>>
>>>
>>> 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
>>>>
>>>
>