linux-kernel - Re: [PATCH] [v3] spi: work around clang bug in SPI_BPW_RANGE

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Message-ID: <CAMuHMdWv3On3w9hqJUZ7oKNHxphhNZNN8JhN4oUgfyvu7C9XRg@mail.gmail.com>
Date:   Mon, 11 Mar 2019 10:11:19 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Mark Brown <broonie@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v3] spi: work around clang bug in SPI_BPW_RANGE_MASK()

Hi Arnd,

On Thu, Mar 7, 2019 at 4:55 PM Arnd Bergmann <arnd@...db.de> wrote:
> Clang-8 evaluates both sides of a ?: expression to check for
> valid arithmetic even in the side that is never taken. This
> results in a build warning:
>
> drivers/spi/spi-sh-msiof.c:1052:24: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
>         .bits_per_word_mask = SPI_BPW_RANGE_MASK(8, 32),
>                               ^~~~~~~~~~~~~~~~~~~~~~~~~
>
> Change the implementation to use the GENMASK() macro that does
> what we want here but does not have a problem with the shift
> count overflow.
>
> Link: https://bugs.llvm.org/show_bug.cgi?id=38789
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for your patch!

> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -444,8 +444,7 @@ struct spi_controller {
>         /* bitmask of supported bits_per_word for transfers */
>         u32                     bits_per_word_mask;
>  #define SPI_BPW_MASK(bits) BIT((bits) - 1)
> -#define SPI_BIT_MASK(bits) (((bits) == 32) ? ~0U : (BIT(bits) - 1))
> -#define SPI_BPW_RANGE_MASK(min, max) (SPI_BIT_MASK(max) - SPI_BIT_MASK(min - 1))
> +#define SPI_BPW_RANGE_MASK(min, max) GENMASK((min) - 1, (max) - 1)

Shouldn't that be GENMASK((max) - 1, (min) - 1)?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds