Re: [PATCH v30 15/30] ASoC: usb: Fetch ASoC card and pcm device information

Takashi Iwai
2024-11-20T12:24:03Z

On Wed, 06 Nov 2024 20:33:58 +0100,
Wesley Cheng wrote:
>
> USB SND needs to know how the USB offload path is being routed. This would
> allow for applications to open the corresponding sound card and pcm device
> when it wants to take the audio offload path. This callback should return
> the mapped indexes based on the USB SND device information.
>
> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
> include/sound/soc-usb.h | 16 ++++++++++++++++
> sound/soc/soc-usb.c | 34 ++++++++++++++++++++++++++++++++++
> 2 files changed, 50 insertions(+)
>
> diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
> index 587ea07a8cf5..c3d3e8d62ac5 100644
> --- a/include/sound/soc-usb.h
> +++ b/include/sound/soc-usb.h
> @@ -36,6 +36,11 @@ struct snd_soc_usb_device {
> * @list - list head for SND SOC struct list
> * @component - reference to ASoC component
> * @connection_status_cb - callback to notify connection events
> + * @update_offload_route_info - callback to fetch mapped ASoC card and pcm
> + * device pair. This is unrelated to the concept
> + * of DAPM route. The "route" argument carries
> + * an array used for a kcontrol output and should
> + * contain two integers, card and pcm device index
> * @priv_data - driver data
> **/
> struct snd_soc_usb {
> @@ -44,6 +49,9 @@ struct snd_soc_usb {
> int (*connection_status_cb)(struct snd_soc_usb *usb,
> struct snd_soc_usb_device *sdev,
> bool connected);
> + int (*update_offload_route_info)(struct snd_soc_component *component,
> + int card, int pcm, int direction,
> + long *route);
> void *priv_data;
> };
>
> @@ -61,6 +69,8 @@ int snd_soc_usb_setup_offload_jack(struct snd_soc_component *component,
> int snd_soc_usb_disable_offload_jack(struct snd_soc_component *component);
> int snd_soc_usb_enable_offload_jack(struct snd_soc_component *component,
> struct snd_soc_jack *jack);
> +int snd_soc_usb_update_offload_route(struct device *dev, int card, int pcm,
> + int direction, long *route);
>
> struct snd_soc_usb *snd_soc_usb_allocate_port(struct snd_soc_component *component,
> void *data);
> @@ -109,6 +119,12 @@ static inline int snd_soc_usb_enable_offload_jack(struct snd_soc_component *comp
> return 0;
> }
>
> +static int snd_soc_usb_update_offload_route(struct device *dev, int card, int pcm,
> + int direction, long *route)
> +{
> + return -ENODEV;
> +}
> +
> static inline struct snd_soc_usb *
> snd_soc_usb_allocate_port(struct snd_soc_component *component, void *data)
> {
> diff --git a/sound/soc/soc-usb.c b/sound/soc/soc-usb.c
> index ab914878e101..e56826f1df71 100644
> --- a/sound/soc/soc-usb.c
> +++ b/sound/soc/soc-usb.c
> @@ -145,6 +145,40 @@ int snd_soc_usb_enable_offload_jack(struct snd_soc_component *component,
> }
> EXPORT_SYMBOL_GPL(snd_soc_usb_enable_offload_jack);
>
> +/**
> + * snd_soc_usb_update_offload_route - Find active USB offload path
> + * @dev - USB device to get offload status
> + * @card - USB card index
> + * @pcm - USB PCM device index
> + * @direction - playback or capture direction
> + * @route - pointer to route output array
> + *
> + * Fetch the current status for the USB SND card and PCM device indexes
> + * specified. The "route" argument should be an array of integers being
> + * used for a kcontrol output. The first element should have the selected
> + * card index, and the second element should have the selected pcm device
> + * index.
> + */
> +int snd_soc_usb_update_offload_route(struct device *dev, int card, int pcm,
> + int direction, long *route)
> +{
> + struct snd_soc_usb *ctx;
> + int ret = -EINVAL;
> +
> + ctx = snd_soc_find_usb_ctx(dev);
> + if (!ctx)
> + return -ENODEV;
> +
> + mutex_lock(&ctx_mutex);
> + if (ctx && ctx->update_offload_route_info)
> + ret = ctx->update_offload_route_info(ctx->component, card, pcm,
> + direction, route);
> + mutex_unlock(&ctx_mutex);

The second ctx check is redundant. And the locking scheme looks
dubious -- as ctx isn't protected by ctx_mutex after its retrieval via
snd_soc_find_usb_ctx(), even if you reacquire ctx_mutex, it may point
to an already released object (in theory).

IOW, for a safer protection, you'd need to cover the whole
find-and-exec procedure via a single ctx_mutex lock action.

thanks,

Takashi