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, 3 insertions, 1 deletions

diff --git a/include/sound/memalloc.h b/include/sound/memalloc.h
index 96d0dc171459..d787a6b4a101 100644
--- a/include/sound/memalloc.h
+++ b/include/sound/memalloc.h
@@ -97,7 +97,9 @@ static inline unsigned int snd_sgbuf_aligned_pages(size_t size)
  */
 static inline dma_addr_t snd_sgbuf_get_addr(struct snd_sg_buf *sgbuf, size_t offset)
 {
-	return sgbuf->table[offset >> PAGE_SHIFT].addr + offset % PAGE_SIZE;
+	dma_addr_t addr = sgbuf->table[offset >> PAGE_SHIFT].addr;
+	addr &= PAGE_MASK;
+	return addr + offset % PAGE_SIZE;
 }
 
 /*