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drm/i915: Update comment in vlv_set_rps_idle()

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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>
Link: http://patchwork.freedesktop.org/patch/msgid/20170102152845.32352-1-chris@chris-wilson.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
This commit is contained in:
Chris Wilson 2017-01-02 15:28:45 +00:00
parent bae3fdce06
commit c9efef7bd9
1 changed files with 12 additions and 2 deletions
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14
drivers/gpu/drm/i915/intel_pm.c
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@ -5004,8 +5004,18 @@ 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 committing the voltage change) as that takes a lot less
* power than the render powerwell.
*/
intel_uncore_forcewake_get(dev_priv, FORCEWAKE_MEDIA);
valleyview_set_rps(dev_priv, val);
intel_uncore_forcewake_put(dev_priv, FORCEWAKE_MEDIA);