[Intel-gfx] [PATCH v9] drm/i915: implement EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT

[Atwood, Matthew S]

On Thu, 2018-11-29 at 15:37 -0800, Rodrigo Vivi wrote:
> On Thu, Nov 29, 2018 at 10:54:50PM +0000, Atwood, Matthew S wrote:
> > On Thu, 2018-11-29 at 14:00 -0800, Manasi Navare wrote:
> > > From: Matt Atwood <matthew.s.atwood at intel.com>
> > > 
> > > According to DP spec (2.9.3.1 of DP 1.4) if
> > > EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT is set the addresses
> > > in
> > > DPCD
> > > 02200h through 0220Fh shall contain the DPRX's true capability.
> > > These
> > > values will match 00000h through 0000Fh, except for DPCD_REV,
> > > MAX_LINK_RATE, DOWN_STREAM_PORT_PRESENT.
> > > 
> > > Read from DPCD once for all 3 values as this is an expensive
> > > operation.
> > > Spec mentions that all of address space 02200h through 0220Fh
> > > should
> > > contain the right information however currently only 3 values can
> > > differ.
> > > 
> > > There is no address space in the intel_dp->dpcd struct for
> > > addresses
> > > 02200h through 0220Fh, and since so much of the data is a
> > > identical,
> > > simply overwrite the values stored in 00000h through 0000Fh with
> > > the
> > > values that can be overwritten from addresses 02200h through
> > > 0220Fh.
> > > 
> > > This patch helps with backward compatibility for devices pre
> > > DP1.3.
> > > 
> > > v2: read only dpcd values which can be affected, remove incorrect
> > > check,
> > > split into drm include changes into separate patch, commit
> > > message,
> > > verbose debugging statements during overwrite.
> > > v3: white space fixes
> > > v4: make path dependent on DPCD revision > 1.2
> > > v5: split into function, removed DPCD rev check
> > > v6: add debugging prints for early exit conditions
> > > v7 (From Manasi):
> > > * Memcpy, memcmp and debig logging based on sizeof(dpcd_ext)
> > > (Jani N)
> > > * Exit early (Jani N)
> > > v8 (From Manasi):
> > > * Get rid of superfluous debug prints (Jani N)
> > > * Print entire base DPCD before memcpy (Jani N)
> > > v9 (From Manasi):
> > > * Add uniform newlines (Rodrigo)
> > > 
> > > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > > Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> > > Signed-off-by: Matt Atwood <matthew.s.atwood at intel.com>
> > > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> > > Tested-by: Manasi Navare <manasi.d.navare at intel.com>
> > > Acked-by: Manasi Navare <manasi.d.navare at intel.com>
> > > Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c | 38
> > > +++++++++++++++++++++++++++++++++
> > >  1 file changed, 38 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > > b/drivers/gpu/drm/i915/intel_dp.c
> > > index 38a6e82153fd..b7c4d38089b5 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -3991,6 +3991,42 @@ intel_dp_link_down(struct intel_encoder
> > > *encoder,
> > >  	}
> > >  }
> > >  
> > > +static void
> > > +intel_dp_extended_receiver_capabilities(struct intel_dp
> > > *intel_dp)
> > > +{
> > > +	u8 dpcd_ext[6];
> > > +
> > > +	/*
> > > +	 * Prior to DP1.3 the bit represented by
> > > +	 * DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT was reserved.
> > > +	 * if it is set DP_DPCD_REV at 0000h could be at a value less
> > > than
> > > +	 * the true capability of the panel. The only way to check is
> > > to
> > > +	 * then compare 0000h and 2200h.
> > > +	 */
> > > +	if (!(intel_dp->dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > > +	      DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT))
> > 
> > I strongly disagree with removing the debug statements. While the
> > spec
> > may be clear, real world products have real world gotchas that can
> > silently fail for a long time. The print statements would affect
> > less
> > then 1% of panels. Why can't we support more verbose debugging
> > statements here?
> 
> Well, I'm also in favor of the more verbose approach. Specially with
> so many bad panels we got out there already.
> 
> But in the end if we print all the Base DPCD I believe we
> will have all information we need anyway right?
Sure.
> 
> > > +		return;
> > > +
> > > +	if (drm_dp_dpcd_read(&intel_dp->aux, DP_DP13_DPCD_REV,
> > > +			     &dpcd_ext, sizeof(dpcd_ext)) !=
> > > sizeof(dpcd_ext)) {
> > > +		DRM_ERROR("DPCD failed read at extended
> > > capabilities\n");
> > > +		return;
> > > +	}
> > > +
> > > +	if (intel_dp->dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
> > > +		DRM_DEBUG_KMS("DPCD extended DPCD rev less than base
> > > DPCD rev\n");
> > > +		return;
> > > +	}
> > > +
> > > +	if (!memcmp(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext)))
> > > +		return;
> > > +
> > > +	DRM_DEBUG_KMS("Base DPCD: %*ph\n",
> > > +		      (int)sizeof(intel_dp->dpcd), intel_dp->dpcd);
> > 
> > I'f we're doing a Base DPCD dump to dmesg, might as well do the new
> > one
> > too and have it all in one place.
> 
> I initially had the same feeling here, but then I noticed that
> the new one is printed right after this function is called.
> So I believe this is a clean enough way. But any patch can be on
> top.
You're right this is fine
> 
> > > +
> > > +	memcpy(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext));
> > 
> > I disagree with this method. I specifically did each register that
> > *could* change to avoid panels that may not follow spec. While this
> > is
> > more spec compliant, I'd prefer an approach that doesnt allow the
> > panel
> > to do things improperly.
> 
> I don't have strong feelings on one or the other approach.
> But the situation with the author disagreeing with own patch
> doesn't seem right.
I'm fine with merging it.
> 
> > > +}
> > > +
> > >  bool
> > >  intel_dp_read_dpcd(struct intel_dp *intel_dp)
> > >  {
> > > @@ -3998,6 +4034,8 @@ intel_dp_read_dpcd(struct intel_dp
> > > *intel_dp)
> > >  			     sizeof(intel_dp->dpcd)) < 0)
> > >  		return false; /* aux transfer failed */
> > >  
> > > +	intel_dp_extended_receiver_capabilities(intel_dp);
> > > +
> > >  	DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd),
> > > intel_dp->dpcd);
> > >  
> > >  	return intel_dp->dpcd[DP_DPCD_REV] != 0;
> > 
> > Manasi, thanks for babysitting this patch while I was on vacation.
> 
> maybe we should split in 2 patches for a clean and accurate
> history? :/
Rather just have this done now I think. 
> 
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