Re: [PATCH 3/7] drm/i915: Configure GEN6_RP_DOWN_TIMEOUT on CHV

[Deepak S <deepak.s@linux.intel.com>]

On Monday 19 January 2015 05:20 PM, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> CherryViewA0_iGfx_BIOS_DRIVER_PUNIT_spec_y14w28d5 tells us not to enable
> the RP down timeout interrupt, and says that the timeout value is hence
> not used. We do enable that interrupt currently though, so leaving the
> timeout as 0 results in very poor performance as the GPU frequency keeps
> dropping constantly. So just program the register with the recommended
> value.
>
> Leaving the interrupt enabled doesn't seem to do any harm so far. So
> I've decided to leave it on for now, just to avoid making CHV a
> special case.
>
> This fixes the performance regression from:
>   commit 5a0afd4b78ec23f27f5d486ac3d102c2e8d66bd7
>   Author: Deepak S <deepak.s@linux.intel.com>
>   Date:   Sat Dec 13 11:43:27 2014 +0530
>
>      drm/i915/chv: Use timeout mode for RC6 on chv
>
> Cc: Deepak S <deepak.s@linux.intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/intel_pm.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index ee9a5f9..8c7a07d 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4743,6 +4743,7 @@ static void cherryview_enable_rps(struct drm_device *dev)
>   	I915_WRITE(GEN6_RC_CONTROL, rc6_mode);
>   
>   	/* 4 Program defaults and thresholds for RPS*/
> +	I915_WRITE(GEN6_RP_DOWN_TIMEOUT, 1000000);

I agree programing RP_DOWN_TIMEOUT Can cause the perf issue. I am surprised why we are not seeing similar issues with RC6 EI?

anways, we do not use GEN6_RP_DOWN_TIMEOUT in chv. Programing it's value to default should not harm
Reviewed-by: Deepak S <deepak.s@intel.com>

>   	I915_WRITE(GEN6_RP_UP_THRESHOLD, 59400);
>   	I915_WRITE(GEN6_RP_DOWN_THRESHOLD, 245000);
>   	I915_WRITE(GEN6_RP_UP_EI, 66000);

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