[PATCH v4 04/11] drm: Helper to read max clock rate

[Ville Syrjälä]

On Mon, Jun 06, 2016 at 04:29:06PM +0300, Mika Kahola wrote:
> Helper routine to read out maximum supported pixel rate
> for DisplayPort legay VGA converter or TMDS clock rate
> for other digital legacy converters. The helper returns
> clock rate in kHz.
> 
> Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 28 ++++++++++++++++++++++++++++
>  include/drm/drm_dp_helper.h     |  2 ++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 7d3b245..18b72eb 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -479,6 +479,34 @@ int drm_dp_downstream_type(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
>  }
>  EXPORT_SYMBOL(drm_dp_downstream_type);
>  
> +/**
> + * drm_dp_downstream_max_clock() - extract branch device max
> + *                                 pixel rate for legacy VGA
> + *                                 converter or max TMDS clock
> + *                                 rate for others
> + * @dpcd: DisplayPort configuration data
> + * @port_cap: port capabilities
> + *
> + * Returns max clock in kHz on success or negative error code on failure
> + */
> +int drm_dp_downstream_max_clock(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) {

Could swap this over to an early return and then we don't have to indent
the actual meat of the function.

> +		if (type == DP_DS_PORT_TYPE_VGA)
> +			return port_cap[1] * 8 * 1000;
> +		else if (type != DP_DS_PORT_TYPE_WIRELESS)
> +			return port_cap[1] * 2500;

That's not correct. I suggest a switch() and deal with each type
explicitly.

> +	}
> +
> +	return -EINVAL;

I think I'd return 0 for the "we don't know" case. That way we can use
this directly without worrying about negative values.

> +}
> +EXPORT_SYMBOL(drm_dp_downstream_max_clock);
> +
>  /*
>   * I2C-over-AUX implementation
>   */
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index f290829..c3324d3 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -810,6 +810,8 @@ 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_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_aux_register(struct drm_dp_aux *aux);
>  void drm_dp_aux_unregister(struct drm_dp_aux *aux);
> -- 
> 1.9.1

-- 
Ville Syrjälä
Intel OTC