[Intel-gfx] [PATCH 10/14] drm/i915: Add MIPI_IO WA

[Imre Deak]

On Mon, Jan 16, 2017 at 12:06:56PM +0200, Srinivas, Vidya wrote:
> 
> 
> > -----Original Message-----
> > From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
> > Sent: Friday, January 13, 2017 9:02 PM
> > To: Deak, Imre <imre.deak at intel.com>
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>; Kahola, Mika
> > <mika.kahola at intel.com>; Srinivas, Vidya <vidya.srinivas at intel.com>; intel-
> > gfx at lists.freedesktop.org; Conselvan De Oliveira, Ander
> > <ander.conselvan.de.oliveira at intel.com>; imre.deak at linux.intel.com
> > Subject: Re: [Intel-gfx] [PATCH 10/14] drm/i915: Add MIPI_IO WA
> > 
> > On Fri, Jan 13, 2017 at 05:03:33PM +0200, Imre Deak wrote:
> > > On pe, 2017-01-13 at 09:55 +0200, Jani Nikula wrote:
> > > > On Thu, 12 Jan 2017, Mika Kahola <mika.kahola at intel.com> wrote:
> > > > > This is definitely needed to pass igt test on bxt
> > > > >
> > > > > 'gem_exec_suspend --run-subtest basic-S3'
> > > > >
> > > > > Tested-by: Mika Kahola <mika.kahola at intel.com>
> > > > >
> > > > > On Mon, 2017-01-09 at 14:46 +0530, Vidya Srinivas wrote:
> > > > > > From: Uma Shankar <uma.shankar at intel.com>
> > > > > >
> > > > > > Enable MIPI IO WA for BXT DSI as per bspec.
> > > > > >
> > > > > > Signed-off-by: Uma Shankar <uma.shankar at intel.com>
> > > > > > ---
> > > > > >  drivers/gpu/drm/i915/i915_reg.h  | 3 +++
> > > > > >  drivers/gpu/drm/i915/intel_dsi.c | 9 +++++++++
> > > > > >  2 files changed, 12 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/i915/i915_reg.h
> > > > > > b/drivers/gpu/drm/i915/i915_reg.h index 71b978a..b9d7e98 100644
> > > > > > --- a/drivers/gpu/drm/i915/i915_reg.h
> > > > > > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > > > > > @@ -8301,6 +8301,9 @@ enum {
> > > > > >  #define _BXT_MIPIC_PORT_CTRL
> > 	0x6B8C0
> > > > > >  #define BXT_MIPI_PORT_CTRL(tc)	_MMIO_MIPI(tc,
> > > > > > _BXT_MIPIA_PORT_CTRL, _BXT_MIPIC_PORT_CTRL)
> > > > > >
> > > > > > +#define BXT_P_CR_GT_DISP_PWRON_0_2_0_GTTMMADR
> > 	_MMIO(0
> > > > > > x138090)
> > > >
> > > > Observe that this register is already defined as
> > > > BXT_P_CR_GT_DISP_PWRON, and already used in intel_dpio_phy.c. It
> > > > seems to me changing the bits in this register should be hooked at the
> > dpio level.
> > > >
> > > > Imre?
> > >
> > > At least the RMW access for this register would need locking against a
> > > concurrent access via the DDI encoder enable/disable code?
> > 
> > Full modesets should be serialized by connection_mutex, or perhaps by
> > some other thing with async modesets. Although I have a feeling that if
> > we're doing async modeset commits without locks half the driveer is going to
> > be on fire. Not sure what people are doing/have planned there.

Ok. I assume the async case will need a generic solution then.

> I hope, with the current design, writing to this register from DSI path should
> be okay and we don't need to take any explicit locks. Is this understanding
> correct ?

Yes, based on the above the connection_mutex provides for the
serialization. Just use the existing define as Jani said.

> > >
> > > We should also make sure the IO is turned off during booting/resuming
> > > if DSI won't be used (and so the DSI disable hook won't be called),
> > > see the BSpec "Broxton Sequences to Initialize Display". We could do
> > > this by enabling/disabling the IO via the power well code which would
> > > solve the locking issue too. This would mean using
> > > POWER_DOMAIN_PORT_DSI, or adding a new power domain if diverging
> > from
> > > the BSpec sequence is a problem (would be worth checking with HW
> > > people, since AFAICS we've been doing this so far).
> AFAIK, this will be taken care in BIOS itself if there is no DSI connected.
> If DSI is connected, this can be controlled in DSI disable/enable sequence.

Yes ideally, but checking at least if this is really the case would make
sense. But I'm ok with the current approach for now.

> > >
> > > Btw, what about the 0x160020, 0x160054 regs? According to BSpec we
> > > need to program these too in the same sequence.
> Yes, this is needed. We have a patch for this. Will float the same for review.
> Thanks for the input.

Any reason for having separate patches?

--Imre