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@xxxxxxx>
---
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.
--
2.26.2
