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

[Ben Widawsky <ben@bwidawsk.net>]

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.

-- 
Ben Widawsky, Intel Open Source Technology Center
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