Re: [RFC 19/20] drm/i915/dp: Extract drm_dp_read_dpcd_caps()

[Sean Paul]

On Tue, Aug 11, 2020 at 04:04:56PM -0400, Lyude Paul wrote:
> Since DP 1.3, it's been possible for DP receivers to specify an
> additional set of DPCD capabilities, which can take precedence over the
> capabilities reported at DP_DPCD_REV.
> 
> Basically any device supporting DP is going to need to read these in an
> identical manner, in particular nouveau, so let's go ahead and just move
> this code out of i915 into a shared DRM DP helper that we can use in
> other drivers.
> 
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_dp_helper.c             | 76 +++++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_dp.c     | 60 +---------------
>  drivers/gpu/drm/i915/display/intel_dp.h     |  1 -
>  drivers/gpu/drm/i915/display/intel_lspcon.c |  2 +-
>  include/drm/drm_dp_helper.h                 |  3 +
>  5 files changed, 82 insertions(+), 60 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 0ff2959c8f8e8..f9445915c6c26 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -423,6 +423,82 @@ bool drm_dp_send_real_edid_checksum(struct drm_dp_aux *aux,
>  }
>  EXPORT_SYMBOL(drm_dp_send_real_edid_checksum);
>  
> +static int drm_dp_read_extended_dpcd_caps(struct drm_dp_aux *aux,
> +					  u8 dpcd[DP_RECEIVER_CAP_SIZE])
> +{
> +	u8 dpcd_ext[6];
> +	int ret;
> +
> +	/*
> +	 * 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 (!(dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> +	      DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT))
> +		return 0;
> +
> +	ret = drm_dp_dpcd_read(aux, DP_DP13_DPCD_REV, &dpcd_ext,
> +			       sizeof(dpcd_ext));
> +	if (ret != sizeof(dpcd_ext))
> +		return -EIO;
> +
> +	if (dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
> +		DRM_DEBUG_KMS("%s: Extended DPCD rev less than base DPCD rev (%d > %d)\n",
> +			      aux->name, dpcd[DP_DPCD_REV],
> +			      dpcd_ext[DP_DPCD_REV]);

Might be a good opportunity to convert all of these to drm_dbg_dp()?

> +		return 0;
> +	}
> +
> +	if (!memcmp(dpcd, dpcd_ext, sizeof(dpcd_ext)))
> +		return 0;
> +
> +	DRM_DEBUG_KMS("%s: Base DPCD: %*ph\n",
> +		      aux->name, DP_RECEIVER_CAP_SIZE, dpcd);
> +
> +	memcpy(dpcd, dpcd_ext, sizeof(dpcd_ext));
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_dp_read_dpcd_caps() - read DPCD caps and extended DPCD caps if
> + * available
> + * @aux: DisplayPort AUX channel
> + * @dpcd: Buffer to store the resulting DPCD in
> + *
> + * Attempts to read the base DPCD caps for @aux. Additionally, this function
> + * checks for and reads the extended DPRX caps (%DP_DP13_DPCD_REV) if
> + * present.
> + *
> + * Returns: %0 if the DPCD was read successfully, negative error code
> + * otherwise.
> + */
> +int drm_dp_read_dpcd_caps(struct drm_dp_aux *aux,
> +			  u8 dpcd[DP_RECEIVER_CAP_SIZE])
> +{
> +	int ret;
> +
> +	ret = drm_dp_dpcd_read(aux, DP_DPCD_REV, dpcd, DP_RECEIVER_CAP_SIZE);
> +	if (ret != DP_RECEIVER_CAP_SIZE || dpcd[DP_DPCD_REV] == 0)
> +		return -EIO;
> +
> +	ret = drm_dp_read_extended_dpcd_caps(aux, dpcd);
> +	if (ret < 0)
> +		return ret;

I wonder if we should just go with the "regular" dpcd caps we just read in this
case?

Regardless of my nits,

Reviewed-by: Sean Paul <sean@xxxxxxxxxx>

> +
> +	DRM_DEBUG_KMS("%s: DPCD: %*ph\n",
> +		      aux->name, DP_RECEIVER_CAP_SIZE, dpcd);
> +
> +	if (dpcd[DP_DPCD_REV] == 0)
> +		ret = -EIO;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_dp_read_dpcd_caps);
> +
>  /**
>   * drm_dp_downstream_read_info() - read DPCD downstream port info if available
>   * @aux: DisplayPort AUX channel
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index e343965a483df..230aa0360dc61 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4449,62 +4449,6 @@ intel_dp_link_down(struct intel_encoder *encoder,
>  	}
>  }
>  
> -static void
> -intel_dp_extended_receiver_capabilities(struct intel_dp *intel_dp)
> -{
> -	struct drm_i915_private *i915 = dp_to_i915(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_err(&i915->drm,
> -			"DPCD failed read at extended capabilities\n");
> -		return;
> -	}
> -
> -	if (intel_dp->dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
> -		drm_dbg_kms(&i915->drm,
> -			    "DPCD extended DPCD rev less than base DPCD rev\n");
> -		return;
> -	}
> -
> -	if (!memcmp(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext)))
> -		return;
> -
> -	drm_dbg_kms(&i915->drm, "Base DPCD: %*ph\n",
> -		    (int)sizeof(intel_dp->dpcd), intel_dp->dpcd);
> -
> -	memcpy(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext));
> -}
> -
> -bool
> -intel_dp_read_dpcd(struct intel_dp *intel_dp)
> -{
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -
> -	if (drm_dp_dpcd_read(&intel_dp->aux, 0x000, intel_dp->dpcd,
> -			     sizeof(intel_dp->dpcd)) < 0)
> -		return false; /* aux transfer failed */
> -
> -	intel_dp_extended_receiver_capabilities(intel_dp);
> -
> -	drm_dbg_kms(&i915->drm, "DPCD: %*ph\n", (int)sizeof(intel_dp->dpcd),
> -		    intel_dp->dpcd);
> -
> -	return intel_dp->dpcd[DP_DPCD_REV] != 0;
> -}
> -
>  bool intel_dp_get_colorimetry_status(struct intel_dp *intel_dp)
>  {
>  	u8 dprx = 0;
> @@ -4563,7 +4507,7 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
>  	/* this function is meant to be called only once */
>  	drm_WARN_ON(&dev_priv->drm, intel_dp->dpcd[DP_DPCD_REV] != 0);
>  
> -	if (!intel_dp_read_dpcd(intel_dp))
> +	if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd) != 0)
>  		return false;
>  
>  	drm_dp_read_desc(&intel_dp->aux, &intel_dp->desc,
> @@ -4650,7 +4594,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  {
>  	int ret;
>  
> -	if (!intel_dp_read_dpcd(intel_dp))
> +	if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd))
>  		return false;
>  
>  	/*
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index b901ab850cbd9..0a3af3410d52e 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -99,7 +99,6 @@ bool intel_dp_source_supports_hbr3(struct intel_dp *intel_dp);
>  bool
>  intel_dp_get_link_status(struct intel_dp *intel_dp, u8 *link_status);
>  
> -bool intel_dp_read_dpcd(struct intel_dp *intel_dp);
>  bool intel_dp_get_colorimetry_status(struct intel_dp *intel_dp);
>  int intel_dp_link_required(int pixel_clock, int bpp);
>  int intel_dp_max_data_rate(int max_link_clock, int max_lanes);
> diff --git a/drivers/gpu/drm/i915/display/intel_lspcon.c b/drivers/gpu/drm/i915/display/intel_lspcon.c
> index b781bf4696443..dc1b35559afdf 100644
> --- a/drivers/gpu/drm/i915/display/intel_lspcon.c
> +++ b/drivers/gpu/drm/i915/display/intel_lspcon.c
> @@ -571,7 +571,7 @@ bool lspcon_init(struct intel_digital_port *dig_port)
>  		return false;
>  	}
>  
> -	if (!intel_dp_read_dpcd(dp)) {
> +	if (drm_dp_read_dpcd_caps(&dp->aux, dp->dpcd) != 0) {
>  		DRM_ERROR("LSPCON DPCD read failed\n");
>  		return false;
>  	}
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 0c141fc81aaa8..11649e93e5bb6 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1607,6 +1607,9 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
>  	return drm_dp_dpcd_write(aux, offset, &value, 1);
>  }
>  
> +int drm_dp_read_dpcd_caps(struct drm_dp_aux *aux,
> +			  u8 dpcd[DP_RECEIVER_CAP_SIZE]);
> +
>  int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
>  				 u8 status[DP_LINK_STATUS_SIZE]);
>  
> -- 
> 2.26.2
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS