[Intel-gfx] [PATCH 2/2] drm/i915/tgl: Skip Wa_1604555607 verification at A0

[Tvrtko Ursulin]

On 01/10/2019 18:36, Chris Wilson wrote:
> Quoting Ramalingam C (2019-10-01 18:26:24)
>> Read of FF_MODE2 register is broken at TGL A0. Hence verification of the
>> Wa_1604555607 associated to that register needs to be skipped.
>>
>> Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
>> cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_workarounds.c | 22 ++++++++++++++++++++-
>>   drivers/gpu/drm/i915/i915_drv.h             |  6 ++++++
>>   2 files changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
>> index 4049b876492a..c63d8c3df4d3 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
>> @@ -991,10 +991,21 @@ wa_list_apply(struct intel_uncore *uncore, const struct i915_wa_list *wal)
>>   
>>          for (i = 0, wa = wal->list; i < wal->count; i++, wa++) {
>>                  intel_uncore_rmw_fw(uncore, wa->reg, wa->mask, wa->val);
>> -               if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
>> +               if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)) {
>> +
>> +                       /*
>> +                        * Read of FF_MODE2 is broken on TGL A0.
>> +                        * Hence skip the corresponding WA verification.
>> +                        */
>> +                       if (IS_TGL_REVID(uncore->i915, 0, TGL_REVID_A0) &&
>> +                           i915_mmio_reg_equal(wa->reg, FF_MODE2) &&
>> +                           wa->mask == FF_MODE2_TDS_TIMER_MASK)
>> +                               continue;
> 
> This does not scale very well. You will note that wa_verify() already
> includes a detail on which bits can be read back from HW.

For the record Chris is referring to wa->read which you can set to zero 
for this particular wa and this should automagically work.

Then in IGT/gem_workarounds.c you also have existing framework for 
marking registers as write-only. It may need extending to account for 
steppings and so.

Regards,

Tvrtko