ALSA: Allocate larger pages in sgbuf

Most hardwares have limited buffer-descriptor table length.  This
also restricts the max buffer size of the sound driver.
For example, snd-hda-intel has 1MB buffer size limit, and this is
because it can have at most 256 BDL entries.  For supporting larger
buffers, we need to allocate larger pages even for sg-buffers.

This patch changes the sgbuf allocation code to try to allocate
larger pages first.  At each head of the allocated pages, the
number of allocated pages is stored in the lowest bits of the
corresponding entry of the table addr field.  This change isn't
visible as long as the driver uses snd_sgbuf_get_addr() helper.

Also, the patch adds a new function, snd_pcm_sgbuf_get_chunk_size().
This returns the size of the chunk on continuous pages starting at
the given position offset.  If the chunk reaches to a non-continuous
page, it returns the size to the boundary.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

1 files changed, 26 insertions, 0 deletions

diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c
index 859b118..a6d4280 100644
--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -324,6 +324,32 @@ struct page *snd_pcm_sgbuf_ops_page(struct snd_pcm_substream *substream, unsigne
 
 EXPORT_SYMBOL(snd_pcm_sgbuf_ops_page);
 
+/*
+ * compute the max chunk size with continuous pages on sg-buffer
+ */
+unsigned int snd_pcm_sgbuf_get_chunk_size(struct snd_pcm_substream *substream,
+					  unsigned int ofs, unsigned int size)
+{
+	struct snd_sg_buf *sg = snd_pcm_substream_sgbuf(substream);
+	unsigned int start, end, pg;
+
+	start = ofs >> PAGE_SHIFT;
+	end = (ofs + size - 1) >> PAGE_SHIFT;
+	/* check page continuity */
+	pg = sg->table[start].addr >> PAGE_SHIFT;
+	for (;;) {
+		start++;
+		if (start > end)
+			break;
+		pg++;
+		if ((sg->table[start].addr >> PAGE_SHIFT) != pg)
+			return (start << PAGE_SHIFT) - ofs;
+	}
+	/* ok, all on continuous pages */
+	return size;
+}
+EXPORT_SYMBOL(snd_pcm_sgbuf_get_chunk_size);
+
 /**
  * snd_pcm_lib_malloc_pages - allocate the DMA buffer
  * @substream: the substream to allocate the DMA buffer to