[Intel-gfx] [PATCH v8] drm/i915: implement EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT

[Manasi Navare]

On Thu, Nov 29, 2018 at 11:28:34AM -0800, Rodrigo Vivi wrote:
> On Thu, Nov 29, 2018 at 10:34:05AM -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):
> 
> it seems you should have signed-off this commit.

Oh yes will do

> 
> > * Get rid of superfluous debug prints (Jani N)
> > * Print entire base DPCD before memcpy (Jani N)
> > 
> > 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>
> > 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>
> 
> This changed a lot that I'm not sure my rv-b should remain ;)

Yes agree, i will remove that

> 
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 35 +++++++++++++++++++++++++++++++++
> >  1 file changed, 35 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 70ae3d57316b..5698441abe47 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3802,6 +3802,39 @@ 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))
> > +		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;
> > +	}
> 
> no strong feeling, just yet-another bikesheding:
> but the mix with blank lines and no blank lines is at least strange to my OCD.

Guess the newlines are just residues from spins, will make it uniform

> 
> > +	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);
> > +	memcpy(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext));
> 
> hm... I'm afraid the full copy might be dangerous.

We are not doing full copy here since the size of dpcd_ext is only 6 bytes.
We are only restricting it from 0x2200 to 0x2205

And the reason we are doing all 6 is because memcmp returned that something changed.

Manasi

> 
> 0x2215 to 0x22FF is
> "RESERVED for Extended Receiver V Capability Read all 0s"
> 
> On this range of the original one we have
> 0x0021 which contains DP_MST_CAP bit that we use in our code.
> 
> This full copy seems to have the potential to break MST if not
> more cases.
> 
> I prefer the individual copy of the bits that we know that we need.
> 
> but if you prefer the full copy it seems that it would be better
> to limit memcopy to 0x0015
> 
> Thanks,
> Rodrigo.
> 
> > +}
> > +
> >  bool
> >  intel_dp_read_dpcd(struct intel_dp *intel_dp)
> >  {
> > @@ -3809,6 +3842,8 @@ 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;
> > -- 
> > 2.19.1
> > 
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