ALSA: pcm: introduce INFO_NO_REWINDS flag
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@suse.de>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20211119230852.206310-3-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index fdd9927..f209002 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -2128,6 +2128,7 @@ 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)
@@ -2135,6 +2136,19 @@ 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) {
