ALSA PCM core has an optimized way to communicate with user-space for its control and status data via mmap on the supported architectures like x86. Depending on the situation, however, we'd rather want to enforce user-space notifying the applptr or hwptr change explicitly via ioctl. For example, the upcoming non-contig and non-coherent buffer handling would need an explicit sync, and this needs to catch the applptr and hwptr changes.
This patch adds the new PCM hardware info flag, SNDRV_PCM_INFO_EXPLICIT_SYNC. When this flag is set, PCM core disables both the control and the status mmap, which enforces user-space to update via SYNC_PTR ioctl. In that way, drivers can catch the applptr and hwptr update and apply the sync operation if needed.
Signed-off-by: Takashi Iwai tiwai@suse.de --- include/uapi/sound/asound.h | 1 + sound/core/pcm_native.c | 9 +++++++++ 2 files changed, 10 insertions(+)
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h index d17c061950df..1d84ec9db93b 100644 --- a/include/uapi/sound/asound.h +++ b/include/uapi/sound/asound.h @@ -299,6 +299,7 @@ typedef int __bitwise snd_pcm_subformat_t; #define SNDRV_PCM_INFO_HAS_LINK_ABSOLUTE_ATIME 0x02000000 /* report absolute hardware link audio time, not reset on startup */ #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_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_native.c b/sound/core/pcm_native.c index dc9fa312fadd..d233cb3b41d8 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -3621,6 +3621,12 @@ static int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file
static bool pcm_status_mmap_allowed(struct snd_pcm_file *pcm_file) { + /* If drivers require the explicit sync (typically for non-coherent + * pages), we have to disable the mmap of status and control data + * to enforce the control via SYNC_PTR ioctl. + */ + if (pcm_file->substream->runtime->hw.info & SNDRV_PCM_INFO_EXPLICIT_SYNC) + return false; /* See pcm_control_mmap_allowed() below. * Since older alsa-lib requires both status and control mmaps to be * coupled, we have to disable the status mmap for old alsa-lib, too. @@ -3635,6 +3641,9 @@ static bool pcm_control_mmap_allowed(struct snd_pcm_file *pcm_file) { if (pcm_file->no_compat_mmap) return false; + /* see above */ + if (pcm_file->substream->runtime->hw.info & SNDRV_PCM_INFO_EXPLICIT_SYNC) + return false; /* Disallow the control mmap when SYNC_APPLPTR flag is set; * it enforces the user-space to fall back to snd_pcm_sync_ptr(), * thus it effectively assures the manual update of appl_ptr.