Re: [PATCH] drm/i915/icl: Fix context slice count configuration

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

On 29/08/2018 13:11, Tvrtko Ursulin wrote:
> 
> 
> On 29/08/2018 13:09, Tvrtko Ursulin wrote:
>>
>> On 29/08/2018 13:02, Tvrtko Ursulin wrote:
>>>
>>> On 29/08/2018 12:07, Lionel Landwerlin wrote:
>>>> On 29/08/2018 11:54, Tvrtko Ursulin wrote:
>>>>>
>>>>> On 22/08/2018 17:33, Lionel Landwerlin wrote:
>>>>>> On 22/08/2018 17:18, Tvrtko Ursulin wrote:
>>>>>>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>>>>
>>>>>>> Bitfield width for configuring the active slice count has grown 
>>>>>>> in Gen11
>>>>>>> so we need to program the GEN8_R_PWR_CLK_STATE accordingly.
>>>>>>>
>>>>>>> Current code was always requesting eight times the number of 
>>>>>>> slices (due
>>>>>>> writting to a bitfield starting three bits higher than it 
>>>>>>> should). These
>>>>>>> requests were luckily a) capped by the hardware to the available 
>>>>>>> number of
>>>>>>> slices, and b) we haven't yet exported the code to ask for 
>>>>>>> reduced slice
>>>>>>> configurations.
>>>>>>>
>>>>>>> Due both of the above there was no impact from this incorrect 
>>>>>>> programming
>>>>>>> but we should still fix it.
>>>>>>>
>>>>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>>>> Bspec: 12247
>>>>>>> Reported-by: tony.ye@intel.com
>>>>>>> Suggested-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
>>>>>>> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
>>>>>>> Cc: tony.ye@intel.com
>>>>>>> ---
>>>>>>>   drivers/gpu/drm/i915/i915_reg.h  |  2 ++
>>>>>>>   drivers/gpu/drm/i915/intel_lrc.c | 12 ++++++++----
>>>>>>>   2 files changed, 10 insertions(+), 4 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/i915/i915_reg.h 
>>>>>>> b/drivers/gpu/drm/i915/i915_reg.h
>>>>>>> index 59d06d0055bb..640f7b774a26 100644
>>>>>>> --- a/drivers/gpu/drm/i915/i915_reg.h
>>>>>>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>>>>>>> @@ -344,6 +344,8 @@ static inline bool 
>>>>>>> i915_mmio_reg_valid(i915_reg_t reg)
>>>>>>>   #define   GEN8_RPCS_S_CNT_ENABLE    (1 << 18)
>>>>>>>   #define   GEN8_RPCS_S_CNT_SHIFT        15
>>>>>>>   #define   GEN8_RPCS_S_CNT_MASK        (0x7 << 
>>>>>>> GEN8_RPCS_S_CNT_SHIFT)
>>>>>>> +#define   GEN11_RPCS_S_CNT_SHIFT    12
>>>>>>> +#define   GEN11_RPCS_S_CNT_MASK        (0x3f << 
>>>>>>> GEN11_RPCS_S_CNT_SHIFT)
>>>>>>>   #define   GEN8_RPCS_SS_CNT_ENABLE    (1 << 11)
>>>>>>>   #define   GEN8_RPCS_SS_CNT_SHIFT    8
>>>>>>>   #define   GEN8_RPCS_SS_CNT_MASK        (0x7 << 
>>>>>>> GEN8_RPCS_SS_CNT_SHIFT)
>>>>>>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c 
>>>>>>> b/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>> index 36050f085071..43b8b0675ba0 100644
>>>>>>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>> @@ -2501,10 +2501,14 @@ make_rpcs(struct drm_i915_private *dev_priv)
>>>>>>>        * enablement.
>>>>>>>       */
>>>>>>>       if (INTEL_INFO(dev_priv)->sseu.has_slice_pg) {
>>>>>>> -        rpcs |= GEN8_RPCS_S_CNT_ENABLE;
>>>>>>> -        rpcs |= hweight8(INTEL_INFO(dev_priv)->sseu.slice_mask) <<
>>>>>>> -            GEN8_RPCS_S_CNT_SHIFT;
>>>>>>> -        rpcs |= GEN8_RPCS_ENABLE;
>>>>>>> +        rpcs = hweight8(INTEL_INFO(dev_priv)->sseu.slice_mask);
>>>>>>> +
>>>>>>> +        if (INTEL_GEN(dev_priv) >= 11)
>>>>>>> +            rpcs <<= GEN11_RPCS_S_CNT_SHIFT;
>>>>>>> +        else
>>>>>>> +            rpcs <<= GEN8_RPCS_S_CNT_SHIFT;
>>>>>>> +
>>>>>>> +        rpcs |= GEN8_RPCS_ENABLE | GEN8_RPCS_S_CNT_ENABLE;
>>>>>>
>>>>>>
>>>>>> I don't know if you saw that wording in the documentation :
>>>>>>
>>>>>>   "
>>>>>>
>>>>>> Note: In ICL, software programs this register as if GT consists of 
>>>>>> 2 slices with 4 subslices in each slice. Hardware maps this to the 
>>>>>> 1 slice/8-subslice physical layout.
>>>>>>
>>>>>> "
>>>>>>
>>>>>>
>>>>>> My understanding is that it would make this function a bit more 
>>>>>> complicated ;)
>>>>>>
>>>>>> It also implies that on ICL you cannot select 3 subslices, which 
>>>>>> is unfortunately what Tony was trying to do.
>>>>>>
>>>>>> Maybe some opens need to be raised as to what's possible on ICL.
>>>>>
>>>>> Happy to r-b this one since we clarified it is fine?
>>>>>
>>>>> Regards,
>>>>>
>>>>> Tvrtko
>>>>>
>>>>>
>>>> I think there is still an issue here with regard to the subslice 
>>>> programming.
>>>> You can only program values in [1, 4].
>>>> But because we expose up to 8 subslices, you need to take that mask 
>>>> and alter the slice mask based on its value.
>>>
>>> Hmm true, thanks. I think we need to somehow express this restriction 
>>> on the uAPI level rather than silently mask it. Shall we reject 
>>> attempts to configure subslice mask if hweight(mask) > max_subslices 
>>> / 2 for ICL-LP?
>>
>> No wait, I was in the dynamic sseu world, but this also applies to the 
>> current code base..
>>
>> When we program SScount in drm-tip with the hweight of 8 we overflow 
>> the bitfield already and splat over SScountEn. Luckily with no ill 
>> effect since we set it anyway.
>>
>> So the fix needs to be in make_rpcs today..
>>
>> if (GEN11_LP) {
>>      if (hweight(slice_mask) == 1)
> 
> && hweight(subslice_mask) < max_subslices
> 
> So to leave the default full config alone.

Which means that drm-tip configures the 1x6x8 part as SScount=0b110, 
which is another undocumented value according to BSpec. Furthermore the 
allowed configuration table suggests only three subslices can be enabled 
when SScountEn is set, so like the situation on BXT/GLK, now I need to 
figure out if we are inadvertently only enabling half of the subslices 
on ICL-LP.

Tvrtko

>>          subslice_count /= 2;
>>      else
>>          subslice_en = 0;
>> }
>>
>> I think..
>>
>> Regards,
>>
>> Tvrtko
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