linux-kernel - Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation

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Message-ID: <20170310143241.GJ31469@gate.crashing.org>
Date:   Fri, 10 Mar 2017 08:32:41 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Scott Wood <oss@...error.net>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation

On Fri, Mar 10, 2017 at 03:04:48PM +0100, Christophe LEROY wrote:
> Le 10/03/2017 à 14:06, Segher Boessenkool a écrit :
> >On Fri, Mar 10, 2017 at 11:54:19AM +0100, Christophe LEROY wrote:
> >>gpio_get() and gpio_set() are used extensively by some GPIO based
> >>drivers like SPI, NAND, so it may be worth it as it doesn't impair
> >>readability (if anyone prefers, we could write  (1 << 31) >> i  instead
> >>of  0x80000000 >> i )
> >
> >1 << 31 is undefined behaviour, of course.
> >
> 
> Shall it be 1U << 31 ?

Sure, that works.  "1 << (31 - i)" is most readable (but it doesn't yet
generate the code you want).


Segher