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Re: [PATCH] MIPS: rb532: fix bit swapping in rb532_set_bit()

To: n0-1@freewrt.org
Subject: Re: [PATCH] MIPS: rb532: fix bit swapping in rb532_set_bit()
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Mon, 03 Nov 2008 23:48:56 +0900 (JST)
Cc: ralf@linux-mips.org, sshtylyov@ru.mvista.com, linux-mips@linux-mips.org
In-reply-to: <1225722625-19750-1-git-send-email-n0-1@freewrt.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20081103142942.GA13461@nuty> <1225722625-19750-1-git-send-email-n0-1@freewrt.org>
Sender: linux-mips-bounce@linux-mips.org
On Mon,  3 Nov 2008 15:30:25 +0100, Phil Sutter <n0-1@freewrt.org> wrote:
> The algorithm works unconditionally. If bitval is one, the first line is
> a no op and the second line sets the bit at offset position. Vice versa,
> if bitval is zero, the first line clears the bit at offset position and
> the second line is a no op.

Well, the linux gpio framework uses 0 for low, _nonzero_ for high.
You should not assume the bitval is 0 or 1.

        val &= ~(!bitval << offset);   /* unset bit if bitval == 0 */
        val |= (!!bitval << offset);   /* set bit if bitval != 0 */

would be safe here.  Or you should ensure the bitval is 0 or 1
somewhere.

---
Atsushi Nemoto

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