Re: [PATCH 2/2] drm/i915: implement EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT

["Atwood, Matthew S" <matthew.s.atwood@intel.com>]

On Thu, 2018-07-19 at 14:07 -0700, Rodrigo Vivi wrote:
> On Thu, Jul 19, 2018 at 01:35:49PM -0700, matthew.s.atwood@intel.com
> wrote:
> > From: Matt Atwood <matthew.s.atwood@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
> > 
> > Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 37
> > +++++++++++++++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > index dde92e4af5d3..a31fbbbd7954 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3738,6 +3738,43 @@ intel_dp_read_dpcd(struct intel_dp
> > *intel_dp)
> >  			     sizeof(intel_dp->dpcd)) < 0)
> >  		return false; /* aux transfer failed */
> >  
> 
> We never know what vendors can do with reserved bits. We should never
> assume
> they are zero. So we shouldn't do any of below unless it is newer
> than DP 1.3.
I think you mean newer than DP1.2?
> 
> > +	if (intel_dp->dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > +	    DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT) {
> > +		uint8_t dpcd_ext[6];
> > +
> > +		DRM_DEBUG_KMS("DPCD: Extended Receiver Capability
> > Field Present, accessing 02200h through 022FFh\n");
> > +
> > +		if (drm_dp_dpcd_read(&intel_dp->aux,
> > DP_DP13_DPCD_REV,
> > +				     &dpcd_ext, sizeof(dpcd_ext))
> > < 0)
> > +			return false; /* aux transfer failed */
> > +
> > +		if (memcmp(&intel_dp->dpcd[DP_DPCD_REV],
> > &dpcd_ext[DP_DPCD_REV],
> > +			   sizeof(u8))) {
> > +			DRM_DEBUG_KMS("DPCD: new value for DPCD
> > Revision previous value %2x new value %2x\n",
> > +				      intel_dp->dpcd[DP_DPCD_REV],
> > +				      dpcd_ext[DP_DPCD_REV]);
> > +			memcpy(&intel_dp->dpcd[DP_DPCD_REV],
> > +			       &dpcd_ext[DP_DPCD_REV],
> > +			       sizeof(u8));
> > +		}
> > +		if (memcmp(&intel_dp->dpcd[DP_MAX_LINK_RATE],
> > +			   &dpcd_ext[DP_MAX_LINK_RATE],
> > sizeof(u8))) {
> > +			DRM_DEBUG_KMS("DPCD: new value for DPCD
> > Max Link Rate previous value %2x new value %2x\n",
> > +				      intel_dp-
> > >dpcd[DP_MAX_LINK_RATE],
> > +				      dpcd_ext[DP_MAX_LINK_RATE]);
> > +			memcpy(&intel_dp->dpcd[DP_MAX_LINK_RATE],
> > +			       &dpcd_ext[DP_MAX_LINK_RATE],
> > sizeof(u8));
> > +		}
> > +		if (memcmp(&intel_dp-
> > >dpcd[DP_DOWNSTREAMPORT_PRESENT],
> > +			   &dpcd_ext[DP_DOWNSTREAMPORT_PRESENT],
> > sizeof(u8))) {
> > +			DRM_DEBUG_KMS("DPCD: new value for DPCD
> > Downstream Port Present  previous value %2x new value %2x\n",
> > +				      intel_dp-
> > >dpcd[DP_DOWNSTREAMPORT_PRESENT],
> > +				      dpcd_ext[DP_DOWNSTREAMPORT_P
> > RESENT]);
> > +			memcpy(&intel_dp-
> > >dpcd[DP_DOWNSTREAMPORT_PRESENT],
> > +			       &dpcd_ext[DP_DOWNSTREAMPORT_PRESENT
> > ],
> > +			       sizeof(u8));
> > +		}
> > +	}
> >  	DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp-
> > >dpcd), intel_dp->dpcd);
> >  
> >  	return intel_dp->dpcd[DP_DPCD_REV] != 0;
> > -- 
> > 2.17.1
> > 
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