[PATCH v4 02/11] drm: Read DP downstream port capabilities

[Ville Syrjälä]

On Mon, Jun 06, 2016 at 04:29:04PM +0300, Mika Kahola wrote:
> Read DisplayPort downstream port capabilities. Depending on
> the DP port the capabilities are defined in length of 1 byte
> or 4 bytes depending if the detailed capability information is
> available.
> 
> Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 27 +++++++++++++++++++++++++++
>  include/drm/drm_dp_helper.h     |  3 +++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index eeaf5a7..c4149fd 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -438,6 +438,33 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
>  }
>  EXPORT_SYMBOL(drm_dp_link_configure);
>  
> +/**
> + * drm_dp_downstream_port_cap() - read downstream port capabilities
> + * @dpcd: DisplayPort configuration data
> + * @port_cap: port capabilities
> + *
> + * returns size of the port capabilites
> + */
> +int drm_dp_downstream_port_cap(struct drm_dp_aux *aux,
> +			       const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> +			       u8 port_cap[4])
> +{
> +	int size;
> +	bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> +		DP_DETAILED_CAP_INFO_AVAILABLE;
> +
> +	if (detailed_cap_info) {
> +		size = 4;
> +		drm_dp_dpcd_read(aux, DP_DOWNSTREAM_PORT_0, port_cap, size);
> +	} else {
> +		size = 1;
> +		drm_dp_dpcd_read(aux, DP_DOWNSTREAM_PORT_0, &port_cap[0], size);
> +	}

Could avoid a bit of duplicatetion. Eg.:
	if (dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE)
		size = 4;
	else
		size = 1;

	return drm_dp_dpcd_read(...);

Though perhaps we should just read out the entire 4/16 bytes to get the
caps for all the ports?

> +
> +	return size;
> +}
> +EXPORT_SYMBOL(drm_dp_downstream_port_cap);
> +
>  /*
>   * I2C-over-AUX implementation
>   */
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index e384c7f..db8d3d47 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -806,6 +806,9 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
>  int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
>  int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link);
>  int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
> +int drm_dp_downstream_port_cap(struct drm_dp_aux *aux,
> +			       const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> +			       u8 port_cap[4]);
>  
>  int drm_dp_aux_register(struct drm_dp_aux *aux);
>  void drm_dp_aux_unregister(struct drm_dp_aux *aux);
> -- 
> 1.9.1

-- 
Ville Syrjälä
Intel OTC