[Intel-gfx] [PATCH 03/12] drm/i915: Simplify VLV drain latency computation

[Jesse Barnes]

On 02/10/2015 05:28 AM, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> The current drain lantency computation relies on hardcoded limits to
> determine when the to use the low vs. high precision multiplier.
> Rewrite the code to use a more straightforward approach.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 0f0281a..d6c6c1b 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -727,12 +727,15 @@ static bool vlv_compute_drain_latency(struct drm_crtc *crtc,
>  		return false;
>  
>  	entries = DIV_ROUND_UP(clock, 1000) * pixel_size;
> -	if (IS_CHERRYVIEW(dev))
> -		*prec_mult = (entries > 32) ? 16 : 8;
> -	else
> -		*prec_mult = (entries > 128) ? 64 : 32;
> +
> +	*prec_mult = IS_CHERRYVIEW(dev) ? 16 : 64;
>  	*drain_latency = (64 * (*prec_mult) * 4) / entries;
>  
> +	if (*drain_latency > DRAIN_LATENCY_MASK) {
> +		*prec_mult /= 2;
> +		*drain_latency = (64 * (*prec_mult) * 4) / entries;
> +	}
> +
>  	if (*drain_latency > DRAIN_LATENCY_MASK)
>  		*drain_latency = DRAIN_LATENCY_MASK;
>  
> 

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