[Intel-gfx] [PATCH] drm/i915/vlv: drop punit freq staus read after setting idle

[Lee, Chon Ming]

On 06/12 08:14, S, Deepak wrote:
> 
> 
> On 6/11/2014 10:26 PM, Ville Syrjälä wrote:
> >On Fri, Jun 06, 2014 at 08:03:20AM -0700, Jesse Barnes wrote:
> >>On Fri, 6 Jun 2014 11:29:24 +0300
> >>Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> >>
> >>>On Thu, Jun 05, 2014 at 01:49:34PM -0700, Jesse Barnes wrote:
> >>>>This may take awhile (~10ms), and we don't need to make noise about it.
> >>>>
> >>>>References: https://bugs.freedesktop.org/show_bug.cgi?id=75244
> >>>>Tested-by: huax.lu at intel.com
> >>>>Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> >>>>---
> >>>>  drivers/gpu/drm/i915/intel_pm.c | 4 ----
> >>>>  1 file changed, 4 deletions(-)
> >>>>
> >>>>diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> >>>>index ee27d74..4eebfd8 100644
> >>>>--- a/drivers/gpu/drm/i915/intel_pm.c
> >>>>+++ b/drivers/gpu/drm/i915/intel_pm.c
> >>>>@@ -3227,10 +3227,6 @@ static void vlv_set_rps_idle(struct drm_i915_private *dev_priv)
> >>>>  	vlv_punit_write(dev_priv, PUNIT_REG_GPU_FREQ_REQ,
> >>>>  					dev_priv->rps.min_freq_softlimit);
> >>>>
> >>>>-	if (wait_for(((vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS))
> >>>>-				& GENFREQSTATUS) == 0, 5))
> >>>>-		DRM_ERROR("timed out waiting for Punit\n");
> >>>>-
> >>>
> >>>As I recall the entire point of this was to make sure the frequency
> >>>really drops before we allow turning off the clock. I'm not sure if we
> >>>can trust that the frequency (and more importantly the voltage) will
> >>>drop if we allow turning off the clock before the transition is
> >>>complete.
> >>
> >>well, we may need to increase the timeout then... let's see if that
> >>helps with the bug.
> >
> >FYI I played around with my BYT a bit and it doesn't appear to require
> >this "force gfx clock on" part of the workaround.
> >
> >I was polling VLV_GTLC_SURVIVABILITY_REG and VLV_GTLC_PW_STATUS to make
> >sure both render and media wells and the gfx clock remain off, and I
> >was also monitoring vnn via svid. While that was going on I just rewrote
> >PUNIT_REG_GPU_FREQ_REQ to make Punit change the frequency, and sure
> >enough it did, and svid showed me that vnn had also changed. So it
> >appears there's no need to have the gfx clock on to change its frequency
> >on this BYT.
> >
> >I wonder if this part of the workaround was only needed on older parts.
> >Deepak, any ideas?
> 
> Yes ville, this was added initial for older parts and force gfx
> clock was part of the workaround.
> We have not verified this on newer parts. Let me check with hw guys
> to see if workaround still exits and when this was fixed.
> 
> Thanks
> Deepak

This is a bit side topic.  In the vlv_set_rps_idle, it try to mask the turbo
interrupt by writing to GEN6_PMINTRMSK (offset 0xA168).  But based on the bspec,
the PMIMR for BYT/GEN6 should be 0x44024 (GEN6_PMIMR).  

Not sure I miss anything.  If there offset is wrong, mean the turbo has not mask at
all.

Regards,
Chon Ming

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