RE: [Intel-gfx] [PATCH 1/4] drm/i915: Disable DC states around GMBUS on GLK

["Runyan, Arthur J" <arthur.j.runyan@intel.com>]

You're right.  DC5 could disrupt GMBUS.  We forgot to add a note on GMBUS when it got moved under DMC domain in GLK and BXT/APL.  I'll take care of that.

-----Original Message-----
From: Ville Syrj�l� [mailto:ville.syrjala@linux.intel.com] 
Sent: Monday, 11 December, 2017 11:03 AM
To: Pandiyan, Dhinakaran <dhinakaran.pandiyan@intel.com>
Cc: intel-gfx@lists.freedesktop.org; stable@vger.kernel.org; Runyan, Arthur J <arthur.j.runyan@intel.com>
Subject: Re: [Intel-gfx] [PATCH 1/4] drm/i915: Disable DC states around GMBUS on GLK

On Mon, Dec 11, 2017 at 06:41:05PM +0000, Pandiyan, Dhinakaran wrote:
> On Fri, 2017-12-08 at 23:37 +0200, Ville Syrjala wrote:
> > From: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> > 
> > Prevent the DMC from destroying GMBUS transfers on GLK. GMBUS
> > lives in PG1 so DC off is all we need.
> > 
> Just so that I understand this correctly. DMC is expected to take care
> of managing power for GMBUS transfers without the driver explicitly
> turning on/off the power well 1 but it isn't. Do you know if this is a
> DMC regression?

No idea. The docs don't seem to even mention DMC and GMBUS in the same
sentence. But since DP AUX needs DC off I don't see why GMBUS would
be all that different.

And with bit banging I would be somewhat surprised if DMC could
maintain the state of the pins while in DC5. Although I suppose it
might be possible that the hw automagically prevents DC5 when we're
driving any of the pins.

Art?

> 
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_runtime_pm.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
> > index 96ab74f3d101..522e0a63090f 100644
> > --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
> > @@ -1792,6 +1792,7 @@ void intel_display_power_put(struct drm_i915_private *dev_priv,
> >  	BIT_ULL(POWER_DOMAIN_GT_IRQ) |			\
> >  	BIT_ULL(POWER_DOMAIN_MODESET) |			\
> >  	BIT_ULL(POWER_DOMAIN_AUX_A) |			\
> > +	BIT_ULL(POWER_DOMAIN_GMBUS) |			\
> >  	BIT_ULL(POWER_DOMAIN_INIT))
> >  
> >  #define CNL_DISPLAY_POWERWELL_2_POWER_DOMAINS (		\

-- 
Ville Syrj�l�
Intel OTC