[Intel-gfx] [RFC 3/4] drm/i915: valleyview: Make intel_set_rps get FORCEWAKE_MEDIA

[Chris Wilson]

On Sun, Jan 01, 2017 at 09:48:53PM +0100, Hans de Goede wrote:
> Hi,
> 
> On 01-01-17 21:24, Chris Wilson wrote:
> >On Sun, Jan 01, 2017 at 09:14:02PM +0100, Hans de Goede wrote:
> >>All callers of valleyview_set_rps() get at least FORCEWAKE_MEDIA, except
> >>for intel_set_rps(). Since intel_set_rps can for example be called from
> >>sysfs store functions, there is no guarantee this is already done, so add
> >>an intel_uncore_forcewake_get(FORCEWAKE_MEDIA) call to intel_set_rps.
> >>
> >>Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >>---
> >> drivers/gpu/drm/i915/intel_pm.c | 9 +++++++--
> >> 1 file changed, 7 insertions(+), 2 deletions(-)
> >>
> >>diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> >>index 4b12637..cc4fbd7 100644
> >>--- a/drivers/gpu/drm/i915/intel_pm.c
> >>+++ b/drivers/gpu/drm/i915/intel_pm.c
> >>@@ -5096,9 +5096,14 @@ void gen6_rps_boost(struct drm_i915_private *dev_priv,
> >>
> >> void intel_set_rps(struct drm_i915_private *dev_priv, u8 val)
> >> {
> >>-	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
> >>+	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
> >>+		/* Wake up the media well, as that takes a lot less
> >>+		 * power than the Render well.
> >>+		 */
> >>+		intel_uncore_forcewake_get(dev_priv, FORCEWAKE_MEDIA);
> >> 		valleyview_set_rps(dev_priv, val);
> >
> >Both powerwells are woken for rps. (Taking one but not the other has no
> >benefit, and very misleading.)
> 
> The comment on why FORCEWAKE_MEDIA is used + code is copy pasted from the
> existing code in vlv_set_rps_idle().

It's not correct there either...
 
> > The forcewake is already held by the
> >lower level routines, taking the wakelock in the caller is an optimisation
> >that is only interesting if there is a danger from the forcewake being
> >dropped mid-sequence (due to preemption whatever).
> 
> We're also accessing the punit in valleyview_set_rps() and I've seen several
> patches (in the android x86 kernel) suggesting that we need to take a wakelock
> while doing this.

It is quite likely that we do have to guarantee to keep the punit awake
during long sequences. That would be an acceptable rationale (but not in
the caller!).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre