Re: [PATCH 1/6] drm/i915: Bring UP Power Wells before disabling RC6.

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Apr 09, 2014 at 09:51:38AM +0530, S, Deepak wrote:
> 
> 
> On 4/9/2014 9:43 AM, Ben Widawsky wrote:
> >On Tue, Apr 08, 2014 at 06:22:52PM +0530, S, Deepak wrote:
> >>
> >>
> >>On 4/8/2014 6:13 PM, Ville Syrjälä wrote:
> >>>On Mon, Apr 07, 2014 at 02:36:20PM -0700, Ben Widawsky wrote:
> >>>>On Mon, Apr 07, 2014 at 05:01:46PM -0300, Rodrigo Vivi wrote:
> >>>>>From: Deepak S <deepak.s@intel.com>
> >>>>>
> >>>>>We need do forcewake before Disabling RC6, This is what the BIOS
> >>>>>expects while going into suspend.
> >>>>>
> >>>>>v2: updated commit message. (Daniel)
> >>>>>
> >>>>>Signed-off-by: Deepak S <deepak.s@intel.com>
> >>>>>Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
> >>>>>---
> >>>>>  drivers/gpu/drm/i915/intel_pm.c | 6 ++++++
> >>>>>  1 file changed, 6 insertions(+)
> >>>>>
> >>>>>diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> >>>>>index 04af065..ad2ff99 100644
> >>>>>--- a/drivers/gpu/drm/i915/intel_pm.c
> >>>>>+++ b/drivers/gpu/drm/i915/intel_pm.c
> >>>>>@@ -3198,8 +3198,14 @@ static void valleyview_disable_rps(struct drm_device *dev)
> >>>>>  {
> >>>>>  	struct drm_i915_private *dev_priv = dev->dev_private;
> >>>>>
> >>>>>+	/* we're doing forcewake before Disabling RC6,
> >>>>>+	 * This what the BIOS expects when going into suspend */
> >>>>>+	gen6_gt_force_wake_get(dev_priv, FORCEWAKE_ALL);
> >>>>>+
> >>>>>  	I915_WRITE(GEN6_RC_CONTROL, 0);
> >>>>>
> >>>>>+	gen6_gt_force_wake_put(dev_priv, FORCEWAKE_ALL);
> >>>>>+
> >>>>>  	gen6_disable_rps_interrupts(dev);
> >>>>>  }
> >>>>>
> >>>>
> >>>>Isn't the forcewake done as part of I915_WRITE sufficient?
> >>>
> >>>Writes don't do forcewake, nor is the register even part of the
> >>>VLV forcewake ranges.
> >>>
> >>>I guess the rationale for this patche is still a bit vague. But if it's
> >>>really needed, I wonder whether we should do this same dance for !VLV
> >>>too? Do we have any "GPU stuck in wrong power state after suspend" type of
> >>>bugs still around?
> >>
> >>One of suggestion form the HW team was to Bring the wells up before we
> >>disable RC6 at run-time. We did see some issue when we enabled D0ix.
> >>
> >>I think the is a good practice to make sure we bring-up the wells before we
> >>disable RC6. At least this avoids the cases where wells are not up before we
> >>can access the Next register after disable.
> >
> >Ville was totally right. I do think a POSTING_READ is still sufficient.
> >Don't care much either way.
> >
> 
> If feel this patch is not adding any value. I OK dropping this patch.

I think it makes a lot of sense - on the enable side we also grab the
wells (in case the bios has enabled rc6 already) to make sure we change
the rc6/rps state while everything is around.

Can you please update your patch to also roll this out for gen6/8 rps
disable functions?

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch