From: robherring2@gmail•com (Rob Herring)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM: decompressor: clear SCTLR.A bit for v7 cores
Date: Thu, 11 Oct 2012 08:31:47 -0500 [thread overview]
Message-ID: <5076CA43.9070503@gmail.com> (raw)
In-Reply-To: <20121011130955.GP4625@n2100.arm.linux.org.uk>
On 10/11/2012 08:09 AM, Russell King - ARM Linux wrote:
> On Thu, Oct 11, 2012 at 07:43:22AM -0500, Rob Herring wrote:
>> The contents of this were already reviewed on this thread, so I sent this
>> to the patch system and this was Russell's reply:
>
> So that's why I couldn't find it - the mailing list thread has a different
> subject line to the patch. Don't do that. Given the amount of list
> traffic we have today, that's as good as not having been posted at all.
>
>>> NAK for two reasons.
>>>
>>> 1. It hasn't been on the list (I can't find a match for "clear SCTLR.A"
>>> in my mailbox)
>>>
>>> 2. The behaviour of unaligned accesses vary depending on CPU. Some
>>> fix-up the access, others load the word and then rotate it. If we have
>>> decompressors which perform unaligned accesses, we need to fix this
>>> properly to avoid the CPU specific behaviour, rather than tweaking
>>> control bits to hide the problem.
>>
>> I'm simply matching the behavior of the kernel itself. The A bit is cleared
>> for v7 kernels and compilers only generate unaligned accesses for v7.
>> Without this the initial state of the A bit is undefined as a bootloader
>> could have cleared it already. We should document the required state or set
>> it to what we want.
>
> Irrespective of this, (2) still stands. Unaligned accesses in the
> decompressor without a fixup (which will be very hard to provide)
> will return different data depending on the CPU as I mention in point
> 2.
This only affects v7 cores. It should not vary for v7 cores as unaligned
access is a required feature. So how is it going to vary on v7 CPUs?
We've got bigger problems if there are v7 cores that don't handle
unaligned accesses.
Rob
> So, using unaligned accesses in the decompressor may not give expected
> results in all cases, so they're best avoided.
>
> And if they're avoided, then we don't care about the setting of the A
> bit.
>
next prev parent reply other threads:[~2012-10-11 13:31 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-05 1:23 [PATCH v2 0/5] Use more asm-generic headers Rob Herring
2012-08-05 1:23 ` [PATCH v2 1/5] ARM: use generic version of identical asm headers Rob Herring
2012-08-05 1:23 ` [PATCH v2 2/5] ARM: add strstr declaration for decompressors Rob Herring
2012-08-05 1:23 ` [PATCH v2 3/5] ARM: use generic unaligned.h Rob Herring
2012-10-08 16:43 ` Shawn Guo
2012-10-08 20:34 ` Rob Herring
2012-10-08 23:28 ` Shawn Guo
2012-10-09 2:27 ` Rob Herring
2012-10-09 2:45 ` Shawn Guo
2012-10-09 4:01 ` Nicolas Pitre
2012-10-10 13:29 ` Rob Herring
2012-10-10 13:57 ` Nicolas Pitre
2012-10-11 12:43 ` [PATCH] ARM: decompressor: clear SCTLR.A bit for v7 cores Rob Herring
2012-10-11 13:09 ` Russell King - ARM Linux
2012-10-11 13:31 ` Rob Herring [this message]
2012-10-11 13:41 ` Russell King - ARM Linux
2012-10-11 15:44 ` Nicolas Pitre
2012-10-23 20:32 ` Gregory CLEMENT
2012-10-25 12:07 ` Russell King - ARM Linux
2012-10-11 13:59 ` Russell King - ARM Linux
2012-10-11 15:58 ` Nicolas Pitre
2012-10-25 9:34 ` Johannes Stezenbach
2012-10-25 12:41 ` Rob Herring
2012-10-25 13:30 ` Arnd Bergmann
2012-10-25 14:16 ` Johannes Stezenbach
2012-10-25 14:25 ` Rob Herring
2012-10-25 15:02 ` Nicolas Pitre
2012-10-25 15:08 ` Johannes Stezenbach
2012-11-05 10:48 ` Dave Martin
2012-11-05 11:13 ` Russell King - ARM Linux
2012-11-05 13:02 ` Dave Martin
2012-11-05 13:43 ` Johannes Stezenbach
2012-11-05 15:39 ` Russell King - ARM Linux
2012-11-05 16:13 ` Nicolas Pitre
2012-11-05 17:26 ` Dave Martin
2012-11-05 17:44 ` Rob Herring
2012-11-05 20:02 ` Nicolas Pitre
2012-11-05 17:46 ` Nicolas Pitre
2012-11-05 13:48 ` Rob Herring
2012-11-05 22:02 ` Michael Hope
2013-02-20 14:56 ` Johannes Stezenbach
2013-02-20 15:07 ` Johannes Stezenbach
2012-08-05 1:23 ` [PATCH v2 4/5] ARM: use generic termios.h Rob Herring
2012-08-05 1:24 ` [PATCH v2 5/5] ARM: convert asm/irqflags.h to use asm-generic/irqflags.h Rob Herring
2012-08-05 9:34 ` [PATCH v2 0/5] Use more asm-generic headers Thomas Petazzoni
2012-08-06 14:35 ` Arnd Bergmann
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