From: Ramesh Babu ramesh.babu@intel.com
In case of mmap, by default alsa-lib mmaps both control & status data.
If driver subscribes for .appl_ptr_update, driver needs to get notification whenever appl ptr changes. So with control & status mmaped, driver won't get appl ptr notifications.
In alsa-lib IOCTL_SYNC_PTR can be forced using sync_ptr_ioctl flag in conf But this makes driver behavior dependent on a flag in the conf.
This patch conditionally checks for .appl_ptr_update and returns error when user land asks for mmaping control & status data, thus forcing user to issue IOCTL_SYNC_PTR.
One drawback with this approach is, if .appl_ptr_update is subscribed by driver, the user space looses flexibility to mmap the control & status data.
Signed-off-by: Ramesh Babu ramesh.babu@intel.com Signed-off-by: Subhransu S. Prusty subhransu.s.prusty@intel.com --- sound/core/pcm_native.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index c56d4ed..1965d83 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -3535,10 +3535,22 @@ static int snd_pcm_mmap(struct file *file, struct vm_area_struct *area) case SNDRV_PCM_MMAP_OFFSET_STATUS: if (pcm_file->no_compat_mmap) return -ENXIO; + /* + * we want to force sync pointer, + * if driver implements appl_ptr_update + */ + if (substream->ops->appl_ptr_update) + return -ENXIO; return snd_pcm_mmap_status(substream, file, area); case SNDRV_PCM_MMAP_OFFSET_CONTROL: if (pcm_file->no_compat_mmap) return -ENXIO; + /* + * we want to force sync pointer, + * if driver implements appl_ptr_update + */ + if (substream->ops->appl_ptr_update) + return -ENXIO; return snd_pcm_mmap_control(substream, file, area); default: return snd_pcm_mmap_data(substream, file, area);