[Intel-gfx] [PATCH] drm/i915/bxt: Enable VBT based BL control for DP

[Imre Deak]

On Tue, Jun 06, 2017 at 05:58:43PM +0300, Bloomfield, Jon wrote:
> > -----Original Message-----
> > From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On Behalf
> > Of Imre Deak
> > Sent: Tuesday, June 6, 2017 5:34 AM
> > To: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: intel-gfx at lists.freedesktop.org; Mustaffa, Mustamin B
> > <mustamin.b.mustaffa at intel.com>
> > Subject: Re: [Intel-gfx] [PATCH] drm/i915/bxt: Enable VBT based BL control
> > for DP
> > 
> > On Tue, Jun 06, 2017 at 12:24:30PM +0300, Jani Nikula wrote:
> > > On Tue, 06 Jun 2017, Mustamin B Mustaffa
> > <mustamin.b.mustaffa at intel.com> wrote:
> > > > [...]
> > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > > > index d1670b8..124f58b 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > @@ -591,13 +591,8 @@ bxt_power_sequencer_idx(struct intel_dp
> > *intel_dp)
> > > >  	/* We should never land here with regular DP ports */
> > > >  	WARN_ON(!is_edp(intel_dp));
> > > >
> > > > -	/*
> > > > -	 * TODO: BXT has 2 PPS instances. The correct port->PPS instance
> > > > -	 * mapping needs to be retrieved from VBT, for now just hard-code
> > to
> > > > -	 * use instance #0 always.
> > > > -	 */
> > > >  	if (!intel_dp->pps_reset)
> > > > -		return 0;
> > > > +		return dev_priv->vbt.backlight.controller;
> > >
> > > So the existing code around here looks a bit convoluted, not least
> > > because now pretty much all PPS access first does
> > >
> > >  - intel_pps_get_registers(), which calls
> > >  - bxt_power_sequencer_idx(), which calls
> > >  - intel_dp_init_panel_power_sequencer_registers(), which calls
> > >  - intel_pps_get_registers()...
> > >
> > > With your change, for controller == 1 and pps_reset == true, the first
> > > time the registers are needed, we'll initialize the correct controller 1
> > > registers, but controller 0 registers are returned. From there on, we'll
> > > keep returning controller 1 registers until pps_reset is set to true
> > > again.
> > >
> > > Cc: Imre as author of commits 78597996370c ("drm/i915/bxt: Fix PPS lost
> > > state after suspend breaking eDP link training") and 8e8232d51878
> > > ("drm/i915: Deduplicate PPS register retrieval") which I think create
> > > the loop.
> > 
> > A loop would be prevented by the pps->reset check, but agree the code
> > isn't nice, I guess I overlooked this when I wrote it. To make things
> > clearer we could factor out a helper from
> > intel_dp_init_panel_power_sequencer_registers() that takes pps_registers
> > and call this helper from bxt_power_sequencer_idx().
> > 
> > So how about something like the following:
> 
> Just checking what the intention is here because your proposed change
> ommits the VBT fix...  Are you going to post these changes as a new
> baseline for Mustaffa's patch ? Or are you asking Mustaffa to fold
> these changes into his patch ? Hoping it's the former :-)

The change is just to make the code clearer, unrelated to the VBT fix,
so it should be a separate patch. I don't mind doing this as a follow-up
to Mustaffa's patchset. What his patch here would need is just to return 
the correct index from bxt_power_sequencer_idx() in all cases.

--Imre