Messages in this thread | | | Date | Fri, 25 Jun 2021 09:45:48 +0200 | From | Takashi Iwai <> | Subject | Re: [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config |
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On Thu, 24 Jun 2021 23:20:48 +0200, Nathan Chancellor wrote: > > 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@kernel.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);
That's still too error-prone.
Could you rather introduce another variable of u16 * type, and use it instead? Ditto for u8 access for the code after that, too.
thanks,
Takashi
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