From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe LEROY <christophe.leroy@c-s.fr>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, Scott Wood <oss@buserror.net>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation
Date: Fri, 10 Mar 2017 09:41:39 -0600 [thread overview]
Message-ID: <20170310154139.GM31469@gate.crashing.org> (raw)
In-Reply-To: <777e903f-b816-5efa-2ece-e4e16fab27c6@c-s.fr>
On Fri, Mar 10, 2017 at 03:41:23PM +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).
>
> Euh .... I'm a bit lost. Do you mean the form we have today is the
> driver is wrong ?
Heh, yes. But is't okay with GCC, so don't worry about it.
The point is that "0x80000000 >> i" is less readable.
Segher
next prev parent reply other threads:[~2017-03-10 15:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-09 9:42 [PATCH] powerpc: sysdev: cpm1: Optimise gpio bit calculation Christophe Leroy
2017-03-10 8:41 ` Michael Ellerman
2017-03-10 10:54 ` Christophe LEROY
2017-03-10 13:06 ` Segher Boessenkool
2017-03-10 14:04 ` Christophe LEROY
2017-03-10 14:32 ` Segher Boessenkool
2017-03-10 14:41 ` Christophe LEROY
2017-03-10 15:41 ` Segher Boessenkool [this message]
2017-03-21 15:04 ` Christophe LEROY
2017-03-10 13:02 ` Segher Boessenkool
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