Re: [RFC 16/20] drm/i915/dp: Extract drm_dp_get_sink_count()

[Sean Paul]

On Tue, Aug 11, 2020 at 04:04:53PM -0400, Lyude Paul wrote:
> And of course, we'll also need to read the sink count from other drivers
> as well if we're checking whether or not it's supported. So, let's
> extract the code for this into another helper.
> 
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_dp_helper.c         | 20 ++++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_dp.c | 17 +++++------------
>  include/drm/drm_dp_helper.h             |  1 +
>  3 files changed, 26 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 05bb47e589731..0ff2959c8f8e8 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -722,6 +722,26 @@ bool drm_dp_has_sink_count(struct drm_connector *connector,
>  }
>  EXPORT_SYMBOL(drm_dp_has_sink_count);
>  
> +/**
> + * drm_dp_get_sink_count() - Retrieve the sink count for a given sink
> + * @aux: The DP AUX channel to use
> + *
> + * Returns: The current sink count reported by @aux, or a negative error code
> + * otherwise.
> + */
> +int drm_dp_get_sink_count(struct drm_dp_aux *aux)
> +{
> +	u8 count;
> +	int ret;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_SINK_COUNT, &count);
> +	if (ret < 1)
> +		return -EIO;

This should probably be:
        if (ret < 0)
                return ret;
        else if (ret != 1)
                return -EIO;


> +
> +	return DP_GET_SINK_COUNT(count);
> +}
> +EXPORT_SYMBOL(drm_dp_get_sink_count);
> +
>  /*
>   * I2C-over-AUX implementation
>   */
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 35a4779a442e2..e343965a483df 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -4648,6 +4648,8 @@ intel_dp_has_sink_count(struct intel_dp *intel_dp)
>  static bool
>  intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  {
> +	int ret;
> +
>  	if (!intel_dp_read_dpcd(intel_dp))
>  		return false;
>  
> @@ -4664,20 +4666,10 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  	}
>  
>  	if (intel_dp_has_sink_count(intel_dp)) {
> -		u8 count;
> -		ssize_t r;
> -
> -		r = drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT, &count);
> -		if (r < 1)
> +		ret = drm_dp_get_sink_count(&intel_dp->aux);
> +		if (ret < 0)
>  			return false;
>  
> -		/*
> -		 * Sink count can change between short pulse hpd hence
> -		 * a member variable in intel_dp will track any changes
> -		 * between short pulse interrupts.
> -		 */

I think you could probably keep this comment and relocate the intel_dp->sink_count
assignment back.

With these nits (or something like them),

Reviewed-by: Sean Paul <sean@xxxxxxxxxx>

> -		intel_dp->sink_count = DP_GET_SINK_COUNT(count);
> -
>  		/*
>  		 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
>  		 * a dongle is present but no display. Unless we require to know
> @@ -4685,6 +4677,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  		 * downstream port information. So, an early return here saves
>  		 * time from performing other operations which are not required.
>  		 */
> +		intel_dp->sink_count = ret;
>  		if (!intel_dp->sink_count)
>  			return false;
>  	}
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index a1413a531eaf4..0c141fc81aaa8 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1635,6 +1635,7 @@ struct drm_dp_desc;
>  bool drm_dp_has_sink_count(struct drm_connector *connector,
>  			   const u8 dpcd[DP_RECEIVER_CAP_SIZE],
>  			   const struct drm_dp_desc *desc);
> +int drm_dp_get_sink_count(struct drm_dp_aux *aux);
>  
>  void drm_dp_remote_aux_init(struct drm_dp_aux *aux);
>  void drm_dp_aux_init(struct drm_dp_aux *aux);
> -- 
> 2.26.2
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS