2 files changed, 22 insertions, 2 deletions

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index fd41697cb4d3..7eee52eb7462 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -268,6 +268,7 @@ typedef int __bitwise snd_pcm_subformat_t;
 #define SNDRV_PCM_INFO_MMAP_VALID       0x00000002      /* period data are valid during transfer */
 #define SNDRV_PCM_INFO_DOUBLE           0x00000004      /* Double buffering needed for PCM start/stop */
 #define SNDRV_PCM_INFO_BATCH            0x00000010      /* double buffering */
+#define SNDRV_PCM_INFO_SYNC_APPLPTR     0x00000020      /* need the explicit sync of appl_ptr update */
 #define SNDRV_PCM_INFO_INTERLEAVED      0x00000100      /* channels are interleaved */
 #define SNDRV_PCM_INFO_NONINTERLEAVED   0x00000200      /* channels are not interleaved */
 #define SNDRV_PCM_INFO_COMPLEX          0x00000400      /* complex frame organization (mmap only) */
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index d35c6614fdab..9ade0c8b54a3 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3376,10 +3376,29 @@ static int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file
         area->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
         return 0;
 }
+
+static bool pcm_status_mmap_allowed(struct snd_pcm_file *pcm_file)
+{
+        if (pcm_file->no_compat_mmap)
+                return false;
+        /* Disallow the status/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.
+         * In theory, it should be enough to disallow only PCM control mmap,
+         * but since the current alsa-lib implementation requires both status
+         * and control mmaps always paired, we have to disable both of them.
+         */
+        if (pcm_file->substream->runtime->hw.info & SNDRV_PCM_INFO_SYNC_APPLPTR)
+                return false;
+        return true;
+}
+
 #else /* ! coherent mmap */
 /*
  * don't support mmap for status and control records.
  */
+#define pcm_status_mmap_allowed(pcm_file)       false
+
 static int snd_pcm_mmap_status(struct snd_pcm_substream *substream, struct file *file,
                                struct vm_area_struct *area)
 {
@@ -3563,11 +3582,11 @@ static int snd_pcm_mmap(struct file *file, struct vm_area_struct *area)
         offset = area->vm_pgoff << PAGE_SHIFT;
         switch (offset) {
         case SNDRV_PCM_MMAP_OFFSET_STATUS:
-                if (pcm_file->no_compat_mmap)
+                if (!pcm_status_mmap_allowed(pcm_file))
                         return -ENXIO;
                 return snd_pcm_mmap_status(substream, file, area);
         case SNDRV_PCM_MMAP_OFFSET_CONTROL:
-                if (pcm_file->no_compat_mmap)
+                if (!pcm_status_mmap_allowed(pcm_file))
                         return -ENXIO;
                 return snd_pcm_mmap_control(substream, file, area);
         default: