Re: [RFC v4 16/20] drm/i915/dp: Extract drm_dp_get_sink_count()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 25 Aug 2020, Lyude Paul <lyude@redhat.com> 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.
>
> v2:
> * Fix drm_dp_dpcd_readb() ret check
> * Add back comment and move back sink_count assignment in intel_dp_get_dpcd()
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Sean Paul <sean@poorly.run>
> ---
>  drivers/gpu/drm/drm_dp_helper.c         | 22 ++++++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++------
>  include/drm/drm_dp_helper.h             |  1 +
>  3 files changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 863e0babc1903..67ad05eb05b7e 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -736,6 +736,28 @@ 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

From the department of bikeshedding...

Should we have a naming scheme where it's obvious whether a function
will do DPCD access, or just shuffle existing data?

For example, drm_dp_read_foo() for anything with DPCD access
vs. drm_dp_get_foo() or even simpler for anything that only processes
pre-read data?

> + * @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 < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EIO;

Makes me wonder if that shouldn't be at drm_dp_dpcd_read() level, for
reads returning 0..len-1 bytes. Not necessarily part of this series, but
seems silly to set a precedent to start handling that return value all
over the place.

BR,
Jani.

> +
> +	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..4337321a3be4f 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;
>  
> @@ -4664,11 +4666,8 @@ 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;
>  
>  		/*
> @@ -4676,7 +4675,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
>  		 * a member variable in intel_dp will track any changes
>  		 * between short pulse interrupts.
>  		 */
> -		intel_dp->sink_count = DP_GET_SINK_COUNT(count);
> +		intel_dp->sink_count = ret;
>  
>  		/*
>  		 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
> 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);

-- 
Jani Nikula, Intel Open Source Graphics Center