ALSA: memalloc: Make SG-buffer helper usable for continuous buffer, too

We have a few helper functions for making the access to the buffer
address easier on SG-buffer.  Those are specific to the buffer that is
allocated with SG-buffer type, and it makes hard to use both SG and
non-SG buffers in the same code.

This patch adds a few simple checks and lets the helpers to deal with
both SG- and continuous buffers gracefully.  It's a preliminary step
for the upcoming patch that mimics the buffer type on the fly.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

include/sound/memalloc.h

@@ -94,7 +94,11 @@ static inline dma_addr_t snd_sgbuf_get_addr(struct snd_dma_buffer *dmab,
 					   size_t offset)
 {
 	struct snd_sg_buf *sgbuf = dmab->private_data;
-	dma_addr_t addr = sgbuf->table[offset >> PAGE_SHIFT].addr;
+	dma_addr_t addr;
+
+	if (!sgbuf)
+		return dmab->addr + offset;
+	addr = sgbuf->table[offset >> PAGE_SHIFT].addr;
 	addr &= ~((dma_addr_t)PAGE_SIZE - 1);
 	return addr + offset % PAGE_SIZE;
 }
@@ -106,6 +110,9 @@ static inline void *snd_sgbuf_get_ptr(struct snd_dma_buffer *dmab,
 				     size_t offset)
 {
 	struct snd_sg_buf *sgbuf = dmab->private_data;
+
+	if (!sgbuf)
+		return dmab->area + offset;
 	return sgbuf->table[offset >> PAGE_SHIFT].buf + offset % PAGE_SIZE;
 }
 

sound/core/sgbuf.c

@@ -142,6 +142,9 @@ unsigned int snd_sgbuf_get_chunk_size(struct snd_dma_buffer *dmab,
 	struct snd_sg_buf *sg = dmab->private_data;
 	unsigned int start, end, pg;
 
+	if (!sg)
+		return size;
+
 	start = ofs >> PAGE_SHIFT;
 	end = (ofs + size - 1) >> PAGE_SHIFT;
 	/* check page continuity */