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

[Atwood, Matthew S]

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?
> +		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.
> +
> +	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.
> +}
> +
>  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.