linux-kernel - Re: [ 045/262] ARM: 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores

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Message-ID: <1348921550.18878.1.camel@deadeye.wl.decadent.org.uk>
Date:	Sat, 29 Sep 2012 14:25:50 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Will Deacon <will.deacon@....com>,
	Matthew Leach <matthew.leach@....com>,
	Russell King <rmk+kernel@....linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	alan@...rguk.ukuu.org.uk, Nicolas Pitre <nico@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [ 045/262] ARM: 7501/1: decompressor: reset ttbcr for VMSA
 ARMv7 cores

On Fri, 2012-09-28 at 11:49 -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@...uxfoundation.org>
> 
> 3.5-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Will Deacon <will.deacon@....com>
> 
> commit dbece45894d3ab1baac15a96dc4e1e8e23f64a93 upstream.
> 
> When enabling the MMU for ARMv7 CPUs, the decompressor does not touch
> the ttbcr register, assuming that it will be zeroed (N == 0, EAE == 0).
> Given that only EAE is defined as 0 for non-secure copies of the
> register (and a bootloader such as kexec may leave it set to 1 anyway),
> we should ensure that we reset the register ourselves before turning on
> the MMU.
> 
> This patch zeroes TTBCR.EAE and TTBCR.N prior to enabling the MMU for
> ARMv7 cores in the decompressor, configuring us exclusively for 32-bit
> translation tables via TTBR0.
> 
> Acked-by: Nicolas Pitre <nico@...aro.org>
> Signed-off-by: Matthew Leach <matthew.leach@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[...]

Is this also needed for earlier kernel versions?  If so, can you provide
a backported version?

Ben.

-- 
Ben Hutchings
Usenet is essentially a HUGE group of people passing notes in class.
                      - Rachel Kadel, `A Quick Guide to Newsgroup Etiquette'

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