Re: [Intel-gfx] [PATCH v3 11/11] drm/i915/tgl: Implement Wa_1407901919

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

On Thu, Feb 27, 2020 at 02:01:01PM -0800, José Roberto de Souza wrote:
> This will fix a memory coherence issue.
> 
> v3: using whitespace to make easy to read WA (Chris)
> 
> BSpec: 52890
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_workarounds.c |  8 ++++++++
>  drivers/gpu/drm/i915/i915_reg.h             | 20 +++++++++++---------
>  2 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> index 3e375a3b7714..c59e1a604ab8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> @@ -601,6 +601,14 @@ static void tgl_ctx_workarounds_init(struct intel_engine_cs *engine,
>  	 */
>  	wa_add(wal, FF_MODE2, FF_MODE2_TDS_TIMER_MASK,
>  	       FF_MODE2_TDS_TIMER_128, 0);
> +
> +	/* Wa_1407901919:tgl */
> +	wa_add(wal, ICL_HDC_MODE,
> +	       HDC_COHERENT_ACCESS_L1_CACHE_DIS |
> +	       HDC_DIS_L1_INVAL_FOR_NON_L1_CACHEABLE_W,

I'm not sure if this is what the workaround is asking for.  The way I
understood the workaround, the 2-dword STATE_COMPUTE_MODE instruction
has a couple bits that must be left at 0.  STATE_COMPUTE_MODE is
basically how we ultimately load the HDC_MODE registers (rather than
using a simple LRI like we do for a bunch of other registers), but the
workaround isn't asking us to worry about bits 13+14 in the HDC_MODE
register itself, but rather those flags bits on the instruction that
manipulates the register.

Every time there's a context switch, the hardware will generate a copy
of this instruction as part of the context image in writes to RAM; I'm
assuming these bits aren't set on those hardware-created instructions?
Assuming that's true, then I think this workaround would just be
userspace's responsibility --- if they submit an explicit
STATE_COMPUTE_MODE instruction that isn't just part of the context
image, they need to follow the workaround guidance here and leave two of
those bits set to 0.


Matt

> +	       0,
> +	       HDC_COHERENT_ACCESS_L1_CACHE_DIS |
> +	       HDC_DIS_L1_INVAL_FOR_NON_L1_CACHEABLE_W);
>  }
>  
>  static void
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 80cf02a6eec1..28822585537b 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -7883,15 +7883,17 @@ enum {
>  #define  GEN8_LQSC_FLUSH_COHERENT_LINES		(1 << 21)
>  
>  /* GEN8 chicken */
> -#define HDC_CHICKEN0				_MMIO(0x7300)
> -#define CNL_HDC_CHICKEN0			_MMIO(0xE5F0)
> -#define ICL_HDC_MODE				_MMIO(0xE5F4)
> -#define  HDC_FORCE_CSR_NON_COHERENT_OVR_DISABLE	(1 << 15)
> -#define  HDC_FENCE_DEST_SLM_DISABLE		(1 << 14)
> -#define  HDC_DONOT_FETCH_MEM_WHEN_MASKED	(1 << 11)
> -#define  HDC_FORCE_CONTEXT_SAVE_RESTORE_NON_COHERENT	(1 << 5)
> -#define  HDC_FORCE_NON_COHERENT			(1 << 4)
> -#define  HDC_BARRIER_PERFORMANCE_DISABLE	(1 << 10)
> +#define HDC_CHICKEN0					_MMIO(0x7300)
> +#define CNL_HDC_CHICKEN0				_MMIO(0xE5F0)
> +#define ICL_HDC_MODE					_MMIO(0xE5F4)
> +#define  HDC_FORCE_CSR_NON_COHERENT_OVR_DISABLE		REG_BIT(15)
> +#define  HDC_FENCE_DEST_SLM_DISABLE			REG_BIT(14)
> +#define  HDC_DIS_L1_INVAL_FOR_NON_L1_CACHEABLE_W	REG_BIT(13)
> +#define  HDC_COHERENT_ACCESS_L1_CACHE_DIS		REG_BIT(12)
> +#define  HDC_DONOT_FETCH_MEM_WHEN_MASKED		REG_BIT(11)
> +#define  HDC_FORCE_CONTEXT_SAVE_RESTORE_NON_COHERENT	REG_BIT(5)
> +#define  HDC_FORCE_NON_COHERENT				REG_BIT(4)
> +#define  HDC_BARRIER_PERFORMANCE_DISABLE		REG_BIT(10)
>  
>  #define GEN8_HDC_CHICKEN1			_MMIO(0x7304)
>  
> -- 
> 2.25.1
> 
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-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
(916) 356-2795
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