[alsa-devel] [PATCH] pcm_lib.c: Fixed inaccurate calculation of hw_ptr_interrupt in snd_pcm_update_hw_ptr_interrupt function

[Shine Liu]

There's no restriction on that the runtime->period_size should be the
multiplicator of the runtime->buffer_size in current kernel code.

So "hw_ptr_interrupt = runtime->hw_ptr_interrupt +
runtime->period_size;" is not always the trueth.

I've encounter the problem of this bug, the kernel told me "PCM:
Unexpected hw_pointer value (stream=0, pos=8, intr_ptr=16384)".

The period_size and buffer_size I used was 0x800 and 0x3e80 when the bug
occured.

Following patch will fix the bug.



Signed-off-by: Shine Liu <shinel at foxmail.com>
-----------------------------------------------------------------------

--- a/sound/core/pcm_lib.c	2009-08-14 06:43:34.000000000 +0800
+++ b/sound/core/pcm_lib.c	2009-08-19 17:59:00.000000000 +0800
@@ -248,6 +248,12 @@
 	hw_base = runtime->hw_ptr_base;
 	new_hw_ptr = hw_base + pos;
 	hw_ptr_interrupt = runtime->hw_ptr_interrupt + runtime->period_size;
+	/* if the period_size is not the multiplicator of the 
+ 	 * buffer_size, the hw_ptr_interrupt calculated above 
+ 	 * may not be correct, should be fixed. 
+ 	 */
+	if(hw_ptr_interrupt > hw_base + runtime->buffer_size)
+		hw_ptr_interrupt = hw_base + runtime->buffer_size;
 	delta = new_hw_ptr - hw_ptr_interrupt;
 	if (hw_ptr_interrupt >= runtime->boundary) {
 		hw_ptr_interrupt -= runtime->boundary;