[PATCH v3 2/4] ALSA: pcm: introduce INFO_NO_REWINDS flag

[Takashi Iwai]

On Fri, 15 Oct 2021 21:59:30 +0200,
Pierre-Louis Bossart wrote:
> 
> When the hardware can only deal with a monotonically increasing
> appl_ptr, this flag can be set.
> 
> In case the application requests a rewind, be it with a
> snd_pcm_rewind() or with a direct change of a mmap'ed pointer followed
> by a SNDRV_PCM_IOCTL_SYNC_PTR, this patch checks if a rewind
> occurred and returns an error.
> 
> Credits to Takashi Iwai for identifying the path with SYNC_PTR and
> suggesting the pointer checks.
> 
> Suggested-by: Takashi Iwai <tiwai at suse.de>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> Reviewed-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
> Reviewed-by: Kai Vehmanen <kai.vehmanen at intel.com>

Reviewed-by: Takashi Iwai <tiwai at suse.de>


thanks,

Takashi

> ---
>  include/uapi/sound/asound.h |  2 +-
>  sound/core/pcm_lib.c        | 14 ++++++++++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
> index 5859ca0a1439..59fcf39f022e 100644
> --- a/include/uapi/sound/asound.h
> +++ b/include/uapi/sound/asound.h
> @@ -300,7 +300,7 @@ typedef int __bitwise snd_pcm_subformat_t;
>  #define SNDRV_PCM_INFO_HAS_LINK_ESTIMATED_ATIME    0x04000000  /* report estimated link audio time */
>  #define SNDRV_PCM_INFO_HAS_LINK_SYNCHRONIZED_ATIME 0x08000000  /* report synchronized audio/system time */
>  #define SNDRV_PCM_INFO_EXPLICIT_SYNC	0x10000000	/* needs explicit sync of pointers and data */
> -
> +#define SNDRV_PCM_INFO_NO_REWINDS	0x20000000	/* hardware can only support monotonic changes of appl_ptr */
>  #define SNDRV_PCM_INFO_DRAIN_TRIGGER	0x40000000		/* internal kernel flag - trigger in drain */
>  #define SNDRV_PCM_INFO_FIFO_IN_FRAMES	0x80000000	/* internal kernel flag - FIFO size is in frames */
>  
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index ec53a3e7cf35..1d3927aa3dd8 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -2127,6 +2127,7 @@ int pcm_lib_apply_appl_ptr(struct snd_pcm_substream *substream,
>  {
>  	struct snd_pcm_runtime *runtime = substream->runtime;
>  	snd_pcm_uframes_t old_appl_ptr = runtime->control->appl_ptr;
> +	snd_pcm_sframes_t diff;
>  	int ret;
>  
>  	if (old_appl_ptr == appl_ptr)
> @@ -2134,6 +2135,19 @@ int pcm_lib_apply_appl_ptr(struct snd_pcm_substream *substream,
>  
>  	if (appl_ptr >= runtime->boundary)
>  		return -EINVAL;
> +	/*
> +	 * check if a rewind is requested by the application
> +	 */
> +	if (substream->runtime->info & SNDRV_PCM_INFO_NO_REWINDS) {
> +		diff = appl_ptr - old_appl_ptr;
> +		if (diff >= 0) {
> +			if (diff > runtime->buffer_size)
> +				return -EINVAL;
> +		} else {
> +			if (runtime->boundary + diff > runtime->buffer_size)
> +				return -EINVAL;
> +		}
> +	}
>  
>  	runtime->control->appl_ptr = appl_ptr;
>  	if (substream->ops->ack) {
> -- 
> 2.25.1
>