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

[Pandiyan, Dhinakaran]

On Mon, 2017-12-11 at 23:32 +0000, Runyan, Arthur J wrote:
> 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.
> 

In light of this confirmation, patches 1 and 2 are
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>


> -----Original Message-----
> From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com] 
> Sent: Monday, 11 December, 2017 11:03 AM
> To: Pandiyan, Dhinakaran <dhinakaran.pandiyan at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; stable at vger.kernel.org; Runyan, Arthur J <arthur.j.runyan at 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 Syrjälä <ville.syrjala at 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 at vger.kernel.org
> > > Signed-off-by: Ville Syrjälä <ville.syrjala at 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 (		\
>