[PATCH] ALSA: via82xx: Remove unreachable branch in snd_via686_pcm_pointer()

[PATCH] ALSA: via82xx: Remove unreachable branch in snd_via686_pcm_pointer()

[Evgenii Burenchev]

The condition

	if (count && size < count)

can never evaluate to true.

The VIA DMA count register is masked with 0x00ffffff before use, while
the DMA buffer size is limited to 0x00fffffe bytes. As a result, 'count'
can never exceed 'size', making the condition permanently false.

This branch has therefore been unreachable since the driver was
introduced. Remove the unreachable branch without changing runtime
behavior.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Evgenii Burenchev <evg28bur@yandex.ru>
---
 sound/pci/via82xx_modem.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/sound/pci/via82xx_modem.c b/sound/pci/via82xx_modem.c
index 9b84d3fb9eaf..b32f84ac17cc 100644
--- a/sound/pci/via82xx_modem.c
+++ b/sound/pci/via82xx_modem.c
@@ -573,24 +573,18 @@ static inline unsigned int calc_linear_pos(struct via82xx_modem *chip,
 		       viadev->bufsize2, viadev->idx_table[idx].offset,
 		       viadev->idx_table[idx].size, count);
 #endif
-		if (count && size < count) {
+		if (! count)
+			/* bogus count 0 on the DMA boundary? */
+			res = viadev->idx_table[idx].offset;
+		else
+			/* count register returns full size
+			 * when end of buffer is reached
+			 */
+			res = viadev->idx_table[idx].offset + size;
+		if (check_invalid_pos(viadev, res)) {
 			dev_dbg(chip->card->dev,
-				"invalid via82xx_cur_ptr, using last valid pointer\n");
+				"invalid via82xx_cur_ptr (2), using last valid pointer\n");
 			res = viadev->lastpos;
-		} else {
-			if (! count)
-				/* bogus count 0 on the DMA boundary? */
-				res = viadev->idx_table[idx].offset;
-			else
-				/* count register returns full size
-				 * when end of buffer is reached
-				 */
-				res = viadev->idx_table[idx].offset + size;
-			if (check_invalid_pos(viadev, res)) {
-				dev_dbg(chip->card->dev,
-					"invalid via82xx_cur_ptr (2), using last valid pointer\n");
-				res = viadev->lastpos;
-			}
 		}
 	}
 	viadev->lastpos = res; /* remember the last position */
-- 
2.43.0

Re: [PATCH] ALSA: via82xx: Remove unreachable branch in snd_via686_pcm_pointer()

[Takashi Iwai]

On Mon, 06 Jul 2026 15:16:34 +0200,
Evgenii Burenchev wrote:
> 
> The condition
> 
> 	if (count && size < count)
> 
> can never evaluate to true.
> 
> The VIA DMA count register is masked with 0x00ffffff before use, while
> the DMA buffer size is limited to 0x00fffffe bytes. As a result, 'count'
> can never exceed 'size', making the condition permanently false.
> 
> This branch has therefore been unreachable since the driver was
> introduced. Remove the unreachable branch without changing runtime
> behavior.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Evgenii Burenchev <evg28bur@yandex.ru>

Applied now.  Thanks.


Takashi