[alsa-devel] [PATCH v3 1/4] ALSA: pcm: add IEC958 channel status control helper

[Takashi Iwai]

On Tue, 01 Mar 2016 09:19:14 +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 at st.com>

What is the reason to make the mutex pointer instead of the own one?
Any need for sharing the mutex?

And, if it has to be assigned explicitly by user, you have to write it
explicitly, too.

Another small nitpicking:

> ---
>  include/sound/pcm_iec958.h |  15 +++++++
>  sound/core/pcm_iec958.c    | 107 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 122 insertions(+)
> 
> diff --git a/include/sound/pcm_iec958.h b/include/sound/pcm_iec958.h
> index 0eed397..08e4bab 100644
> --- a/include/sound/pcm_iec958.h
> +++ b/include/sound/pcm_iec958.h
> @@ -3,7 +3,22 @@
>  
>  #include <linux/types.h>
>  
> +/*
> + * IEC 60958 controls parameters
> + * Describes channel status and associated callback
> + */
> +struct snd_pcm_iec958_params {
> +	/* call under mutex protection, when control is updated by user */
> +	int (*ctrl_set)(void *pdata, u8 *status);
> +
> +	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_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 36b2d7a..80e7e47 100644
> --- a/sound/core/pcm_iec958.c
> +++ b/sound/core/pcm_iec958.c
> @@ -7,10 +7,93 @@
>   */
>  #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_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;
> +}

No static?


> +
> +/**
> + * IEC958 channel status default controls callbacks
> + *
> + * Callbacks are protected by a mutex provided by user.
> + */

You don't need the kernel-doc comment "/**" for static functions, in
general.  It's basically for API, not for internal ones.

> +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)
> +		return -EINVAL;
> +
> +	mutex_lock(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];

A loop might be better :)  Let compiler optimize it.

> +	mutex_unlock(params->mutex);
> +
> +	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)
> +		return -EINVAL;
> +
> +	mutex_lock(params->mutex);
> +	if (params->ctrl_set)
> +		err = params->ctrl_set(params->pdata,
> +				       uctl->value.iec958.status);

So, in your design, ctrl_set isn't mandatory?

> +	if (err < 0) {
> +		mutex_unlock(params->mutex);
> +		return 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];
> +
> +	mutex_unlock(params->mutex);
> +
> +	return 1;

Strictly speaking, the return value of put callback should be zero if
the value isn't changed.  This will avoid the ctl value change
notification.


> +}
> +
> +static const struct snd_kcontrol_new iec958_ctls[] = {
> +	{
> +		.access = (SNDRV_CTL_ELEM_ACCESS_READWRITE |
> +			   SNDRV_CTL_ELEM_ACCESS_VOLATILE),
> +		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
> +		.name = SNDRV_CTL_NAME_IEC958("", PLAYBACK, DEFAULT),
> +		.info = snd_pcm_iec958_info,
> +		.get = snd_pcm_iec958_get,
> +		.put = snd_pcm_iec958_put,
> +	},
> +	{
> +		.access = (SNDRV_CTL_ELEM_ACCESS_READ |
> +			   SNDRV_CTL_ELEM_ACCESS_VOLATILE),
> +		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
> +		.name = SNDRV_CTL_NAME_IEC958("", CAPTURE, DEFAULT),
> +		.info = snd_pcm_iec958_info,
> +		.get = snd_pcm_iec958_get,
> +	},
> +};
> +
>  /**
>   * snd_pcm_create_iec958_consumer - create consumer format IEC958 channel status
>   * @runtime: pcm runtime structure with ->rate filled in
> @@ -93,3 +176,27 @@ int snd_pcm_create_iec958_consumer(struct snd_pcm_runtime *runtime, u8 *cs,
>  	return len;
>  }
>  EXPORT_SYMBOL(snd_pcm_create_iec958_consumer);
> +
> +/**
> + * snd_pcm_create_iec958_ctl - create IEC958 channel status default control
> + * pcm: pcm device to associate to the control.
> + * iec958: snd_pcm_iec958_params structure that contains callbacks
> + *         and channel status buffer
> + * stream: stream type SNDRV_PCM_STREAM_PLAYBACK or SNDRV_PCM_STREAM_CATURE

Put "@" prefix for arguments in kernel-doc.

> + * Returns:  negative error code if something failed.
> + */
> +int snd_pcm_create_iec958_ctl(struct snd_pcm *pcm,
> +			      struct snd_pcm_iec958_params *params, int stream)
> +{
> +	struct snd_kcontrol_new knew;
> +
> +	if (stream > SNDRV_PCM_STREAM_LAST)
> +		return -EINVAL;
> +
> +	knew = iec958_ctls[stream];
> +	knew.device = pcm->device;
> +	knew.index = pcm->device;
> +	knew.count = pcm->streams[stream].substream_count;

Hmm, this doesn't always work.  It will create the substream_count
ctls starting from the pcm dev# as index.  What if there are 2 PCM
devices where both contain 4 substreams?

I admit that the current ctl <-> PCM mapping is messing.  There are
some heuristics and you're trying to follow that.  But blindly
applying to all cases doesn't seem to work.


thanks,

Takashi