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Subject[PATCH v5] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config
Date
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. This is not a bug in practice
because count is not greater than one at the moment but this could
change in the future so this should be fixed.

Replace the cast with a temporary variable of the proper type, which is
less error prone and fixes the iteration. Do the same thing for the
'u8 *' below this if block.

Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion")
Link: https://github.com/ClangBuiltLinux/linux/issues/1408
Acked-by: Geoffrey D. Bennett <g@b4.vu>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---

v1 -> v2:

* Use temporary variables of proper type rather than casting, as
requested by Takashi.

* Mention that there is not a bug at the moment per Geoffrey's comment.

v2 -> v3:

* Restrict scope of buf_16 more, as requested by Geoffrey.

* Add Geoffrey's ack.

v3 -> v4:

* Fix stray newline added below

if (config_item->size >= 8) {

leftover from buf_16's declaration.

v4 -> v5 (or how many times does it take Nathan to get a patch right):

* Re-add note about no bug that was dropped in v3 by accident, as
noticed by Geoffrey. My apologies for the multiple revisions.

sound/usb/mixer_scarlett_gen2.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index fcba682cd422..161d832cafef 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -1177,6 +1177,7 @@ static int scarlett2_usb_get_config(
const struct scarlett2_config *config_item =
&scarlett2_config_items[info->has_mixer][config_item_num];
int size, err, i;
+ u8 *buf_8;
u8 value;

/* For byte-sized parameters, retrieve directly into buf */
@@ -1185,9 +1186,12 @@ static int scarlett2_usb_get_config(
err = scarlett2_usb_get(mixer, config_item->offset, buf, size);
if (err < 0)
return err;
- if (size == 2)
- for (i = 0; i < count; i++, (u16 *)buf++)
- *(u16 *)buf = le16_to_cpu(*(__le16 *)buf);
+ if (size == 2) {
+ u16 *buf_16 = buf;
+
+ for (i = 0; i < count; i++, buf_16++)
+ *buf_16 = le16_to_cpu(*(__le16 *)buf_16);
+ }
return 0;
}

@@ -1197,8 +1201,9 @@ static int scarlett2_usb_get_config(
return err;

/* then unpack from value into buf[] */
+ buf_8 = buf;
for (i = 0; i < 8 && i < count; i++, value >>= 1)
- *(u8 *)buf++ = value & 1;
+ *buf_8++ = value & 1;

return 0;
}
base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4
--
2.32.0.93.g670b81a890

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