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Date: Thu, 7 Mar 2019 14:22:59 +0100 From: Arnd Bergmann <arnd@...db.de> To: Rasmus Villemoes <linux@...musvillemoes.dk> Cc: Mark Brown <broonie@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Geert Uytterhoeven <geert@...ux-m68k.org>, Boris Brezillon <bbrezillon@...nel.org>, Marco Felsch <m.felsch@...gutronix.de>, Frieder Schrempf <frieder.schrempf@...eet.de>, 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] spi: work around clang bug in SPI_BPW_RANGE_MASK() On Thu, Mar 7, 2019 at 2:09 PM Rasmus Villemoes <linux@...musvillemoes.dk> wrote: > > On 07/03/2019 11.56, Arnd Bergmann 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 it to shift one less than we want, and then shift one > > more bit afterwards. This should give the correct result for > > all valid input, since it has to be in the range 1..32 anyway. > > Why not use GENMASK which is provided by the same header that #defines BIT? It might be an options, but - I had not thought of it - It looks like it would have the same problem with shifting right by 32 bits (?) - it seems to have slightly different semantics from SPI_BPW_RANGE_MASK(), counting the bits from 0 instead of 1. I tried this version now, which doesn't produce any warnings as far as I can tell, but I'm not convinced that it's actually correct. Can you have a look? #define SPI_BPW_RANGE_MASK(min, max) GENMASK((min) - 1, (max) - 1) Arnd
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