firmware: cs_dsp: Fix fragmentation regression in firmware download

Use vmalloc() instead of kmalloc(..., GFP_DMA) to alloc the temporary
buffer for firmware download blobs. This avoids the problem that a
heavily fragmented system cannot allocate enough physically-contiguous
memory for a large blob.

The redundant alloc buffer mechanism was removed in commit 900baa6
("firmware: cs_dsp: Remove redundant download buffer allocator").
While doing that I was overly focused on the possibility of the
underlying bus requiring DMA-safe memory. So I used GFP_DMA kmalloc()s.
I failed to notice that the code I was removing used vmalloc().
This creates a regression.

Way back in 2014 the problem of fragmentation with kmalloc()s was fixed
by commit cdcd7f7 ("ASoC: wm_adsp: Use vmalloc to allocate firmware
download buffer").

Although we don't need physically-contiguous memory, we don't know if the
bus needs some particular alignment of the buffers. Since the change in
2014, the firmware download has always used whatever alignment vmalloc()
returns. To avoid introducing a new problem, the temporary buffer is still
used, to keep the same alignment of pointers passed to regmap_raw_write().

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 900baa6 ("firmware: cs_dsp: Remove redundant download buffer allocator")
Link: https://patch.msgid.link/20260304141250.1578597-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: rfvirgil

drivers/firmware/cirrus/cs_dsp.c

@@ -1610,11 +1610,17 @@ static int cs_dsp_load(struct cs_dsp *dsp, const struct firmware *firmware,
 			   region_name);
 
 		if (reg) {
+			/*
+			 * Although we expect the underlying bus does not require
+			 * physically-contiguous buffers, we pessimistically use
+			 * a temporary buffer instead of trusting that the
+			 * alignment of region->data is ok.
+			 */
 			region_len = le32_to_cpu(region->len);
 			if (region_len > buf_len) {
 				buf_len = round_up(region_len, PAGE_SIZE);
-				kfree(buf);
-				buf = kmalloc(buf_len, GFP_KERNEL | GFP_DMA);
+				vfree(buf);
+				buf = vmalloc(buf_len);
 				if (!buf) {
 					ret = -ENOMEM;
 					goto out_fw;
@@ -1643,7 +1649,7 @@ static int cs_dsp_load(struct cs_dsp *dsp, const struct firmware *firmware,
 
 	ret = 0;
 out_fw:
-	kfree(buf);
+	vfree(buf);
 
 	if (ret == -EOVERFLOW)
 		cs_dsp_err(dsp, "%s: file content overflows file data\n", file);
@@ -2331,11 +2337,17 @@ static int cs_dsp_load_coeff(struct cs_dsp *dsp, const struct firmware *firmware
 		}
 
 		if (reg) {
+			/*
+			 * Although we expect the underlying bus does not require
+			 * physically-contiguous buffers, we pessimistically use
+			 * a temporary buffer instead of trusting that the
+			 * alignment of blk->data is ok.
+			 */
 			region_len = le32_to_cpu(blk->len);
 			if (region_len > buf_len) {
 				buf_len = round_up(region_len, PAGE_SIZE);
-				kfree(buf);
-				buf = kmalloc(buf_len, GFP_KERNEL | GFP_DMA);
+				vfree(buf);
+				buf = vmalloc(buf_len);
 				if (!buf) {
 					ret = -ENOMEM;
 					goto out_fw;
@@ -2366,7 +2378,7 @@ static int cs_dsp_load_coeff(struct cs_dsp *dsp, const struct firmware *firmware
 
 	ret = 0;
 out_fw:
-	kfree(buf);
+	vfree(buf);
 
 	if (ret == -EOVERFLOW)
 		cs_dsp_err(dsp, "%s: file content overflows file data\n", file);