linux-kernel - [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get

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Message-Id: <20210624212048.1356136-1-nathan@kernel.org>
Date:   Thu, 24 Jun 2021 14:20:48 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     "Geoffrey D. Bennett" <g@...vu>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config

Clang warns:

sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result
unused [-Wunused-value]
                        for (i = 0; i < count; i++, (u16 *)buf++)
                                                    ^      ~~~~~
1 warning generated.

It appears the intention was to cast the void pointer to a u16 pointer
so that the data could be iterated through like an array of u16 values.
However, the cast happens after the increment because a cast is an
rvalue, whereas the post-increment operator only works on lvalues, so
the loop does not iterate as expected.

Replace the post-increment shorthand with the full expression so the
cast can be added in the right place and the look works as expected.

Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion")
Link: https://github.com/ClangBuiltLinux/linux/issues/1408
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 sound/usb/mixer_scarlett_gen2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index fcba682cd422..c20c7f1ddc50 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -1186,7 +1186,7 @@ static int scarlett2_usb_get_config(
 		if (err < 0)
 			return err;
 		if (size == 2)
-			for (i = 0; i < count; i++, (u16 *)buf++)
+			for (i = 0; i < count; i++, buf = (u16 *)buf + 1)
 				*(u16 *)buf = le16_to_cpu(*(__le16 *)buf);
 		return 0;
 	}

base-commit: 5c89c2c7fbfa9124dd521c375b9c82b9ed75bc28
-- 
2.32.0.93.g670b81a890