linux-kernel - Re: [RESEND PATCH 2/2] arm: socfpga: Set share override bit of the l2 cache controller

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Date:	Fri, 20 Feb 2015 07:53:50 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Dinh Nguyen <dinh.linux@...il.com>
Cc:	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RESEND PATCH 2/2] arm: socfpga: Set share override bit of the l2
 cache controller

On Fri, Feb 20, 2015 at 1:15 AM, Dinh Nguyen <dinh.linux@...il.com> wrote:
> Hi Rob,
>
> On 2/19/15 12:13 PM, Rob Herring wrote:
>> On Thu, Feb 19, 2015 at 11:06 AM,  <dinguyen@...nsource.altera.com> wrote:
>>> From: Dinh Nguyen <dinguyen@...nsource.altera.com>
>>>
>>> By not having bit 22 set in the PL310 Auxiliary Control register (shared
>>> attribute override enable) has the side effect of transforming Normal
>>> Shared Non-cacheable reads into Cacheable no-allocate reads.
>>>
>>> Coherent DMA buffers in Linux always have a Cacheable alias via the
>>> kernel linear mapping and the processor can speculatively load cache
>>> lines into the PL310 controller. With bit 22 cleared, Non-cacheable
>>> reads would unexpectedly hit such cache lines leading to buffer
>>> corruption.
>>
>> You really should be doing this in your bootloader.
>>
>
> Can I ask what is your reasoning for doing this in the bootloader? It's
> seems like this is such a nice mechanism to do it here.

Primarily, this register is secure only and we try to avoid secure
mode setup in the kernel.

Russell also has had a patch to do this generically in his patch queue
forever. If we want this in the kernel, then we should apply that.

Rob
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