Re: [PATCH v4 05/11] drm: Helper to read max bits per component

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Jun 06, 2016 at 04:29:07PM +0300, Mika Kahola wrote:
> Helper routine to read out maximum supported bits per
> component for DisplayPort legay converters.
> 
> Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 31 +++++++++++++++++++++++++++++++
>  include/drm/drm_dp_helper.h     |  2 ++
>  2 files changed, 33 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 18b72eb..bac0ccc 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -507,6 +507,37 @@ int drm_dp_downstream_max_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
>  }
>  EXPORT_SYMBOL(drm_dp_downstream_max_clock);
>  
> +/**
> + * drm_dp_downstream_max_bpc() - extract branch device max
> + *                               bits per component
> + * @dpcd: DisplayPort configuration data
> + * @port_cap: port capabilities
> + *
> + * Returns max bpc on success or negative error code on failure
> + */
> +int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> +                              const u8 port_cap[4])
> +{
> +	int type = drm_dp_downstream_type(dpcd, port_cap);
> +	bool detailed_cap_info = dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> +		DP_DETAILED_CAP_INFO_AVAILABLE;
> +
> +	if (detailed_cap_info) {

Early return again.

> +		if (type != DP_DS_PORT_TYPE_WIRELESS) {

switch() again.

> +			int tmp;
> +			tmp = port_cap[2] & DP_DS_VGA_MAX_BPC_MASK;

Should drop the "VGA" from that stuff since it applies to more than
that.

> +
> +			if (tmp == 0)
> +				return 8;
> +			else
> +				return 8 + (1<<tmp);

switch() with each case would be less magicy.

> +		}
> +	}
> +
> +	return -EINVAL;

Again I think I'd just use 0 here.

> +}
> +EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
> +
>  /*
>   * I2C-over-AUX implementation
>   */
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index c3324d3..d4abc38 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -812,6 +812,8 @@ int drm_dp_downstream_port_cap(struct drm_dp_aux *aux,
>  int drm_dp_downstream_type(const u8 dpcd[DP_RECEIVER_CAP_SIZE], const u8 port_cap[4]);
>  int drm_dp_downstream_max_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
>                                  const u8 port_cap[4]);
> +int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> +                              const 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
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