V4L/DVB (6506): saa7134-alsa: Fix mmap support

Trent Piepho wrote:
> 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@ums.usu.ru>
Acked-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/saa7134/saa7134-alsa.c

@@ -543,8 +543,10 @@ static int snd_card_saa7134_hw_params(struct snd_pcm_substream * substream,
 	   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;
 
 }
 
@@ -651,6 +653,17 @@ static int snd_card_saa7134_capture_open(struct snd_pcm_substream * substream)
 	return 0;
 }
 
+/*
+ * 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
  */
@@ -664,6 +677,7 @@ static struct snd_pcm_ops snd_card_saa7134_capture_ops = {
 	.prepare =		snd_card_saa7134_capture_prepare,
 	.trigger =		snd_card_saa7134_capture_trigger,
 	.pointer =		snd_card_saa7134_capture_pointer,
+	.page =			snd_card_saa7134_page,
 };
 
 /*