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-rw-r--r--Documentation/sound/kernel-api/writing-an-alsa-driver.rst4
1 files changed, 4 insertions, 0 deletions
diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
index 5c9523b7d55c..6b8f3495407f 100644
--- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
+++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
@@ -2137,6 +2137,10 @@ This callback is also not mandatory. This callback is called when the
emu10k1-fx and cs46xx need to track the current ``appl_ptr`` for the
internal buffer, and this callback is useful only for such a purpose.
+The callback function may return 0 or a negative error. When the
+return value is ``-EPIPE``, PCM core treats as a buffer XRUN happens,
+and changes the state to ``SNDRV_PCM_STATE_XRUN`` automatically.
+
This callback is atomic as default.
page callback