Re: [PATCH 3/3] drm/i915: Enable GTT caching on gen8

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On 05/19/2015 10:32 AM, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> GTT caching was disabled by default on gen8 due to not working with
> big pages. Some information suggests that it got fixed, but still
> GTT caching has been left disabled by default. Or could be it just
> meant that the default was changed to off, and hence the problem
> got solved.
> 
> Enable GTT caching in the hopes of some performance increase.
> Whether or not the big pages issue has been fixed is irrelevant
> at this stage since we don't use big pages.
> 
> This gives me a 1-2% improvement in xonotic on my BSW. Haven't tried
> BDW, but supposedly it has larger TLBs so might not benefit as much.
> On HSW GTT caching is enabled by default.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h |  2 ++
>  drivers/gpu/drm/i915/intel_pm.c | 13 +++++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 84af255..90640d5 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1461,6 +1461,8 @@ enum skl_disp_power_wells {
>  #define RING_HWS_PGA(base)	((base)+0x80)
>  #define RING_HWS_PGA_GEN6(base)	((base)+0x2080)
>  
> +#define HSW_GTT_CACHE_EN	0x4024
> +#define   GTT_CACHE_EN_ALL	0xF0007FFF
>  #define GEN7_WR_WATERMARK	0x4028
>  #define GEN7_GFX_PRIO_CTRL	0x402C
>  #define ARB_MODE		0x4030
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 5ec56b6..58517a50 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -6205,6 +6205,13 @@ static void broadwell_init_clock_gating(struct drm_device *dev)
>  	I915_WRITE(GEN8_L3SQCREG1, BDW_WA_L3SQCREG1_DEFAULT);
>  	I915_WRITE(GEN7_MISCCPCTL, misccpctl);
>  
> +	/*
> +	 * WaGttCachingOffByDefault:bdw
> +	 * GTT cache may not work with big pages, so if those
> +	 * are ever enabled GTT cache may need to be disabled.
> +	 */
> +	I915_WRITE(HSW_GTT_CACHE_EN, GTT_CACHE_EN_ALL);
> +
>  	lpt_init_clock_gating(dev);
>  }
>  
> @@ -6480,6 +6487,12 @@ static void cherryview_init_clock_gating(struct drm_device *dev)
>  	/* WaDisableSDEUnitClockGating:chv */
>  	I915_WRITE(GEN8_UCGCTL6, I915_READ(GEN8_UCGCTL6) |
>  		   GEN8_SDEUNIT_CLOCK_GATE_DISABLE);
> +
> +	/*
> +	 * GTT cache may not work with big pages, so if those
> +	 * are ever enabled GTT cache may need to be disabled.
> +	 */
> +	I915_WRITE(HSW_GTT_CACHE_EN, GTT_CACHE_EN_ALL);
>  }
>  
>  static void g4x_init_clock_gating(struct drm_device *dev)
> 

Looks ok to me; I guess testing will be the real review here.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
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