Re: [PATCH v2 2/2] drm/i915:gen9: Add disable gather at set shader w/a

["Siluvery, Arun" <arun.siluvery@linux.intel.com>]

On 05/08/2015 15:45, Mika Kuoppala wrote:
> Arun Siluvery <arun.siluvery@linux.intel.com> writes:
>
>> This WA is implemented in init_context as well as WA batch init.
>> There are also some dependent bits need to be set in other registers
>> for this to be complete.
>>
>> v2: behaviour of disable gather at set shader bit can be specified by
>> two different registers, use a better option (Ben).
>>
>
> For me it looks like there are 2 orthogonal goals for this patch.
>
> I think the actual workaround should be one patch, the resetting
> of the set shader bit and the patch named accordingly.
>
> Then the set shader initialization in a different patch,
> if there is justification for it (that I have not managed yet
> to find).

I agree it needs to be split into two patches.

>
> But lets concentrate on the workaround itself...
>
>> Cc: Ben Widawsky <benjamin.widawsky@intel.com>
>> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_reg.h         |  5 +++++
>>   drivers/gpu/drm/i915/intel_lrc.c        |  8 ++++++++
>>   drivers/gpu/drm/i915/intel_ringbuffer.c | 18 ++++++++++++++++++
>>   3 files changed, 31 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>> index 8991cd5..8719a5a 100644
>> --- a/drivers/gpu/drm/i915/i915_reg.h
>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>> @@ -1721,6 +1721,10 @@ enum skl_disp_power_wells {
>>   #define   MEM_DISPLAY_TRICKLE_FEED_DISABLE (1<<2) /* 85x only */
>>   #define FW_BLC		0x020d8
>>   #define FW_BLC2		0x020dc
>> +#define GEN7_RS_CHICKEN  0x20DC
>> +#define   GEN9_RS_CHICKEN_DISABLE_GATHER_AT_SHADER (1<<2)
>> +#define GEN7_FF_SLICE_CHICKEN1    0x20E0
>> +#define   GEN9_PER_CTX_DISABLE_GATHER_CONTROL  (1<<15)
>>   #define FW_BLC_SELF	0x020e0 /* 915+ only */
>>   #define   FW_BLC_SELF_EN_MASK      (1<<31)
>>   #define   FW_BLC_SELF_FIFO_MASK    (1<<16) /* 945 only */
>> @@ -5836,6 +5840,7 @@ enum skl_disp_power_wells {
>>   # define GEN7_CSC1_RHWO_OPT_DISABLE_IN_RCC	((1<<10) | (1<<26))
>>   # define GEN9_RHWO_OPTIMIZATION_DISABLE		(1<<14)
>>   #define COMMON_SLICE_CHICKEN2			0x7014
>> +#define  GEN9_DISABLE_GATHER_SET_SHADER_SLICE   (1<<12)
>>   # define GEN8_CSC2_SBE_VUE_CACHE_CONSERVATIVE	(1<<0)
>>
>>   #define HIZ_CHICKEN					0x7018
>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>> index 9faad82..d3a03f3 100644
>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>> @@ -1292,6 +1292,14 @@ static int gen9_init_perctx_bb(struct intel_engine_cs *ring,
>>   	struct drm_device *dev = ring->dev;
>>   	uint32_t index = wa_ctx_start(wa_ctx, *offset, CACHELINE_DWORDS);
>>
>> +	/* WA to reset "disable gather at set shader slice" bit */
>
> I am thinking how we could also alert the reader that this workaround
> needs to be revisited when it has been given a name.
> By adding WaNoName:skl,bxt along with the comment above?
>
>> +	if (IS_SKYLAKE(dev)) {
>
> As Ben noted, documentation is rather sparse. But the reference
> to previous problems with this bit being save/restored in wrong order,
> we can conclude that this should be for BXT also.
>
>> +		wa_ctx_emit(batch, index, MI_LOAD_REGISTER_IMM(1));
>> +		wa_ctx_emit(batch, index, COMMON_SLICE_CHICKEN2);
>> +		wa_ctx_emit(batch, index,
>> +			    _MASKED_BIT_DISABLE(GEN9_DISABLE_GATHER_SET_SHADER_SLICE));
>> +	}
>> +
>
> The actual value of 'disable set shader' is orthogonal and beyond scope
> of this Workaround so the rest should be strip out to different patch.
>
As you mentioned on irc we first need to know whether we need to disable 
the set shader or not (set ox7014[12:12] to 1), because the WA only 
talks about resetting this bit in per ctx batch.
The following bits can be ignore if there is not need to set that bit in 
the first place.

with reference to gem_ringfill, on my system it only completes without 
any hang if I add this patch completely but on some system this patch 
doesn't seem to be necessary.

regards
Arun

> -Mika
>
>>   	/* WaSetDisablePixMaskCammingAndRhwoInCommonSliceChicken:skl,bxt */
>>   	if ((IS_SKYLAKE(dev) && (INTEL_REVID(dev) <= SKL_REVID_B0)) ||
>>   	    (IS_BROXTON(dev) && (INTEL_REVID(dev) == BXT_REVID_A0))) {
>> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> index dcd1b8f..5e8e5f9 100644
>> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
>> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
>> @@ -985,6 +985,17 @@ static int gen9_init_workarounds(struct intel_engine_cs *ring)
>>   		tmp |= HDC_FORCE_CSR_NON_COHERENT_OVR_DISABLE;
>>   	WA_SET_BIT_MASKED(HDC_CHICKEN0, tmp);
>>
>> +	/* WA to gather at set shader - skl,bxt
>> +	 * These are dependent bits need to be set for the WA.
>> +	 */
>> +	if ((IS_SKYLAKE(dev) && INTEL_REVID(dev) > SKL_REVID_D0) ||
>> +	    (IS_BROXTON(dev) && INTEL_REVID(dev) > BXT_REVID_A0)) {
>> +		WA_SET_BIT_MASKED(GEN7_FF_SLICE_CHICKEN1,
>> +				  GEN9_PER_CTX_DISABLE_GATHER_CONTROL);
>> +		WA_SET_BIT_MASKED(GEN7_RS_CHICKEN,
>> +				  GEN9_RS_CHICKEN_DISABLE_GATHER_AT_SHADER);
>> +	}
>> +
>>   	return 0;
>>   }
>>
>> @@ -1068,6 +1079,13 @@ static int skl_init_workarounds(struct intel_engine_cs *ring)
>>   				  HDC_FENCE_DEST_SLM_DISABLE |
>>   				  HDC_BARRIER_PERFORMANCE_DISABLE);
>>
>> +	/* WA to Disable gather at set shader - skl
>> +	 * This bit needs to be reset in Per ctx WA batch and it is also
>> +	 * dependent on other bits in different register, all of them need
>> +	 * be set for the WA to be complete.
>> +	 */
>> +	WA_SET_BIT_MASKED(COMMON_SLICE_CHICKEN2, GEN9_DISABLE_GATHER_SET_SHADER_SLICE);
>> +
>>   	return skl_tune_iz_hashing(ring);
>>   }
>>
>> --
>> 1.9.1
>>
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>

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