Re: [PATCH 1/2] drm/i915/bdw: Force all Data Cache Data Port access to be Non-Coherent

["Xiang, Haihao" <haihao.xiang@intel.com>]

On Thu, 2013-12-12 at 15:28 -0800, Ben Widawsky wrote: 
> I stumbled on to some unimplemented errata. To be honest, I am not
> really sure of the impact, just that the docs say to do.
> 
> No w/a name for this one.
> 
> Cc: Kenneth Graunke <kenneth@whitecape.org>
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_reg.h | 4 ++++
>  drivers/gpu/drm/i915/intel_pm.c | 7 +++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index e8cc27c..3259e83 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -4167,6 +4167,10 @@
>  #define GEN7_L3SQCREG4				0xb034
>  #define  L3SQ_URB_READ_CAM_MATCH_DISABLE	(1<<27)
>  
> +/* GEN8 chicken */
> +#define HDC_CHICKEN0				0x7300
> +#define  HDC_FORCE_NON_COHERENT			(1<<4)
> +
>  /* WaCatErrorRejectionIssue */
>  #define GEN7_SQ_CHICKEN_MBCUNIT_CONFIG		0x9030
>  #define  GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB	(1<<11)
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index ac9dd46..7e2a0e9 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -5279,6 +5279,13 @@ static void gen8_init_clock_gating(struct drm_device *dev)
>  			   I915_READ(CHICKEN_PIPESL_1(i) |
>  				     DPRS_MASK_VBLANK_SRD));
>  	}
> +
> +	/* Use Force Non-Coherent whenever executing a 3D context. This is a
> +	 * workaround for for a possible hang in the unlikely event a TLB
> +	 * invalidation occurs during a PSD flush.
> +	 */
> +	I915_WRITE(HDC_FORCE_NON_COHERENT,

It should be HDC_CHICKEN0 instead of HDC_FORCE_NON_COHERENT

> +		   I915_READ(HDC_CHICKEN0) | HDC_FORCE_NON_COHERENT);

It has a mask bit which should be set for writing 

> }
>  
>  static void haswell_init_clock_gating(struct drm_device *dev)