[alsa-devel] mmap support in saa7134-alsa (was: Sample format coversion bug?)

[Alexander E. Patrakov]

Trent Piepho wrote:
> On Mon, 29 Oct 2007, Alexander E. Patrakov wrote:
>   
>> Even though mmap seems to be supported in the driver source (judging
>> from .info = SNDRV_PCM_INFO_MMAP | other flags), I could not figure out
>> the parameters that work. Moreover, the driver seems to accept the same
>> hardware parameters without the mmap, and I could not find parameters
>> that the driver accepts for mmap.
>>     
>
> I do not think the saa7134-alsa driver supports mmap.  The cx88-alsa driver
> also claimed to support mmap, but it never worked until I fixed it.  It's
> pretty clear that the code in saa7134-alsa was based on the same code as
> cx88-alsa, so it's likely it has the same bug.
>   

You are right. The patch below (based on your cx88 patch, but I don't 
really understand it) fixes mmap support in saa7134-alsa for me. 
Recording via mmap (arecord -M -f S16_LE -c 2 -r 32000 -D hw:1) didn't 
work at all before, works now, tested for at least 20 minutes (but, 
unfortunately, with one overrun at least 0.719 ms long).

Signed-off-by: Alexander E. Patrakov <patrakov at ums.usu.ru>

--- saa7134-alsa.c	2007-10-12 22:43:44.000000000 +0600
+++ saa7134-alsa.c	2007-10-30 21:01:10.000000000 +0500
@@ -544,8 +544,10 @@
 	   V4L functions, and force ALSA to use that as the DMA area */
 
 	substream->runtime->dma_area = dev->dmasound.dma.vmalloc;
+	substream->runtime->dma_bytes = dev->dmasound.bufsize;
+	substream->runtime->dma_addr = 0;
 
-	return 1;
+	return 0;
 
 }
 
@@ -653,6 +655,17 @@
 }
 
 /*
+ * page callback (needed for mmap)
+ */
+
+static struct page *snd_card_saa7134_page(struct snd_pcm_substream *substream,
+					unsigned long offset)
+{
+	void *pageptr = substream->runtime->dma_area + offset;
+	return vmalloc_to_page(pageptr);
+}
+
+/*
  * ALSA capture callbacks definition
  */
 
@@ -665,6 +678,7 @@
 	.prepare =		snd_card_saa7134_capture_prepare,
 	.trigger =		snd_card_saa7134_capture_trigger,
 	.pointer =		snd_card_saa7134_capture_pointer,
+	.page =			snd_card_saa7134_page,
 };
 
 /*



-- 
Alexander E. Patrakov