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

[Rodrigo Vivi]

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?

> > +		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.

> > +
> > +	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.

> > +}
> > +
> >  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? :/

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