Re: [PATCH] drm/i915: Update comment in vlv_set_rps_idle()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Jan 02, 2017 at 03:28:45PM +0000, Chris Wilson wrote:
> Ville explained that the wakelock was being acquired during set-idle in
> order to flush the voltage change from the punit.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 4406359c5f81..4c9a1b12dfee 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -5011,8 +5011,18 @@ static void vlv_set_rps_idle(struct drm_i915_private *dev_priv)
>  	if (dev_priv->rps.cur_freq <= val)
>  		return;
>  
> -	/* Wake up the media well, as that takes a lot less
> -	 * power than the Render well. */
> +	/* The punit delays the write of the frequency and voltage until it
> +	 * determines the GPU is awake. During normal usage we don't want to
> +	 * waste power changing the frequency if the GPU is sleeping (rc6).
> +	 * However, the GPU and driver is now idle and we do not want to delay
> +	 * switching to minimum voltage (reducing power whilst idle) as we do
> +	 * not expect to be woken in the near future and so must flush the
> +	 * change by waking the device.
> +	 *
> +	 * We choose to take the media powerwell (either would do to trick the
> +	 * punit into commiting the voltage change) as that takes a lot less
> +	 * power than the render powerwell.
> +	 */

lgtm

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_MEDIA);
>  	valleyview_set_rps(dev_priv, val);
>  	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_MEDIA);
> -- 
> 2.11.0

-- 
Ville Syrjälä
Intel OTC
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