From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: lsl / lsr possible confusion in v7_flush_dcache_all
Date: Thu, 8 Sep 2016 10:38:01 +0100 [thread overview]
Message-ID: <20160908093801.GB1493@arm.com> (raw)
In-Reply-To: <20160908091520.GE14909@vsiles-Desktop>
On Thu, Sep 08, 2016 at 11:15:20AM +0200, Vincent Siles wrote:
> While reading the v7_flush_dcache_all (arch/arm/mm/cache-v7.S), I
> stumbled upon this line:
>
> # r10 is the current cache level
> 127: add r2, r10, r10, lsr #1 @ work out 3x current cache level
>
> If we want r2 to be 3 * r10, we should compute r10 + (r10 << 1), which
> is lsl, not lsr.
>
> I check for a recent kernel, the issue seems to still be here:
> repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> revision: d71f058617564750261b673ea9b3352382b9cde4
This code is take pretty much verbatim from the ARM ARM and, despite
being fairly obfuscated, does what it says on the tin. r10 is incremented
by 2 each time round the loop, so this is basically doing 2i + (2i / 2).
Will
WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will.deacon@arm.com>
To: Vincent Siles <vincent.siles@provenrun.com>
Cc: Russell King <linux@armlinux.org.uk>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: lsl / lsr possible confusion in v7_flush_dcache_all
Date: Thu, 8 Sep 2016 10:38:01 +0100 [thread overview]
Message-ID: <20160908093801.GB1493@arm.com> (raw)
In-Reply-To: <20160908091520.GE14909@vsiles-Desktop>
On Thu, Sep 08, 2016 at 11:15:20AM +0200, Vincent Siles wrote:
> While reading the v7_flush_dcache_all (arch/arm/mm/cache-v7.S), I
> stumbled upon this line:
>
> # r10 is the current cache level
> 127: add r2, r10, r10, lsr #1 @ work out 3x current cache level
>
> If we want r2 to be 3 * r10, we should compute r10 + (r10 << 1), which
> is lsl, not lsr.
>
> I check for a recent kernel, the issue seems to still be here:
> repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> revision: d71f058617564750261b673ea9b3352382b9cde4
This code is take pretty much verbatim from the ARM ARM and, despite
being fairly obfuscated, does what it says on the tin. r10 is incremented
by 2 each time round the loop, so this is basically doing 2i + (2i / 2).
Will
next prev parent reply other threads:[~2016-09-08 9:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-08 9:15 lsl / lsr possible confusion in v7_flush_dcache_all Vincent Siles
2016-09-08 9:15 ` Vincent Siles
2016-09-08 9:38 ` Will Deacon [this message]
2016-09-08 9:38 ` Will Deacon
2016-09-08 9:50 ` Vincent Siles
2016-09-08 9:50 ` Vincent Siles
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