[Intel-gfx] [PATCH] drm/i915/cnl: WaForceContextSaveRestoreNonCoherent

[Chris Wilson]

Quoting Rodrigo Vivi (2017-08-23 00:27:15)
> To avoid a potential hang condition with TLB invalidation
> we need to enable masked bit 5 of MMIO 0xE5F0 at boot.
> 
> Same workaround was in place for previous platforms,
> but the change for CNL is more on the register offset.
> But also BSpec doesn't mention the bit 15 as set on gen9
> platforms and mark bit as reserved on CNL.
> 
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Cc: Oscar Mateo <oscar.mateo at intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h        | 1 +
>  drivers/gpu/drm/i915/intel_engine_cs.c | 4 ++++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index d4ecb1905ad8..f31fab2651fb 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -7024,6 +7024,7 @@ enum {
>  
>  /* GEN8 chicken */
>  #define HDC_CHICKEN0                           _MMIO(0x7300)
> +#define CNL_HDC_CHICKEN0                       _MMIO(0xE5F0)
>  #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)
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index d23f18874309..26c35ce5f240 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -1070,6 +1070,10 @@ static int cnl_init_workarounds(struct intel_engine_cs *engine)
>         struct drm_i915_private *dev_priv = engine->i915;
>         int ret;
>  
> +       /* WaForceContextSaveRestoreNonCoherent:cnl */
> +       WA_SET_BIT_MASKED(CNL_HDC_CHICKEN0,
> +                         HDC_FORCE_CONTEXT_SAVE_RESTORE_NON_COHERENT);

This register is not sticky (i.e. does not retain its value even with a
powercontext loaded). Does it even exist?
-Chris