Re: [RFC 2/6] ALSA: pcm: add IEC958 channel status control helper

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Tue, Jan 19, 2016 at 02:40:32PM +0100, Arnaud Pouliquen wrote:
> Add IEC958 channel status helper that creates control to handle the
> IEC60958 status bits.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
> ---
>  include/sound/pcm_iec958.h | 16 +++++++++
>  sound/core/pcm_iec958.c    | 90 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 106 insertions(+)
> 
> diff --git a/include/sound/pcm_iec958.h b/include/sound/pcm_iec958.h
> index 36f023a..7453ace 100644
> --- a/include/sound/pcm_iec958.h
> +++ b/include/sound/pcm_iec958.h
> @@ -3,9 +3,25 @@
>  
>  #include <linux/types.h>
>  
> +/*
> + * IEC 60958 controls parameters
> + * Describes channel status and associated callback
> + */
> +struct snd_pcm_iec958_params {
> +	/* call when control is updated by user */
> +	int (*ctrl_set)(void *pdata, u8 *status, u8 len);
> +
> +	struct snd_aes_iec958 *iec;
> +	void *pdata; /* user private data to retrieve context */
> +	struct mutex *mutex; /* use to avoid race condition */
> +};
> +
>  int snd_pcm_create_iec958_consumer(struct snd_pcm_runtime *runtime, u8 *cs,
>  	size_t len);
>  
>  int snd_pcm_create_iec958_consumer_hw_params(struct snd_pcm_hw_params *params,
>  					     u8 *cs, size_t len);
> +
> +int snd_pcm_create_iec958_ctl(struct snd_pcm *pcm,
> +			      struct snd_pcm_iec958_params *params, int stream);
>  #endif
> diff --git a/sound/core/pcm_iec958.c b/sound/core/pcm_iec958.c
> index c9f8b66..1d426bc 100644
> --- a/sound/core/pcm_iec958.c
> +++ b/sound/core/pcm_iec958.c
> @@ -7,11 +7,78 @@
>   */
>  #include <linux/export.h>
>  #include <linux/types.h>
> +#include <linux/wait.h>
>  #include <sound/asoundef.h>
> +#include <sound/control.h>
>  #include <sound/pcm.h>
>  #include <sound/pcm_params.h>
>  #include <sound/pcm_iec958.h>
>  
> +int snd_pcm_iec958_info(struct snd_kcontrol *kcontrol,
> +			struct snd_ctl_elem_info *uinfo)
> +{
> +	uinfo->type = SNDRV_CTL_ELEM_TYPE_IEC958;
> +	uinfo->count = 1;
> +	return 0;
> +}
> +
> +static int snd_pcm_iec958_get(struct snd_kcontrol *kcontrol,
> +			      struct snd_ctl_elem_value *uctl)
> +{
> +	struct snd_pcm_iec958_params *params = snd_kcontrol_chip(kcontrol);
> +
> +	if (params->mutex)
> +		mutex_unlock(params->mutex);
> +	uctl->value.iec958.status[0] = params->iec->status[0];
> +	uctl->value.iec958.status[1] = params->iec->status[1];
> +	uctl->value.iec958.status[2] = params->iec->status[2];
> +	uctl->value.iec958.status[3] = params->iec->status[3];
> +	uctl->value.iec958.status[4] = params->iec->status[4];
> +	if (params->mutex)
> +		mutex_unlock(params->mutex);

I'm not sure it makes sense for the mutex to be optional.

> +	return 0;
> +}
> +
> +static int snd_pcm_iec958_put(struct snd_kcontrol *kcontrol,
> +			      struct snd_ctl_elem_value *uctl)
> +{
> +	struct snd_pcm_iec958_params *params = snd_kcontrol_chip(kcontrol);
> +	int err = 0;
> +
> +	if (params->mutex)
> +		mutex_lock(params->mutex);
> +	if (params->ctrl_set)
> +		err = params->ctrl_set(params->pdata,
> +				       uctl->value.iec958.status, 5);
> +	if (!err) {
> +		params->iec->status[0] = uctl->value.iec958.status[0];
> +		params->iec->status[1] = uctl->value.iec958.status[1];
> +		params->iec->status[2] = uctl->value.iec958.status[2];
> +		params->iec->status[3] = uctl->value.iec958.status[3];
> +		params->iec->status[4] = uctl->value.iec958.status[4];
> +	}
> +	if (params->mutex)
> +		mutex_unlock(params->mutex);
> +
> +	return 0;

I think you're supposed to report whether anything changed, rather
than just zero on success.

> +}
> +
> +static const struct snd_kcontrol_new iec958_ctls[] = {
> +	{
> +		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
> +		.name = SNDRV_CTL_NAME_IEC958("", PLAYBACK, DEFAULT),

Shouldn't this have a .access member?  What if the audio driver
modifies the IEC958 status for PCM playback - shouldn't it have
the ability to have SNDRV_CTL_ELEM_ACCESS_VOLATILE added?

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