linux-kernel - Re: [PATCH 5/6] ARM: ux500: Enable HIGHMEM on all mop500 platforms

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Message-ID: <5018E11E.7080907@linaro.org>
Date:	Wed, 01 Aug 2012 08:56:14 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	ola.o.lilja@...ricsson.com, alsa-devel@...a-project.org,
	linus.walleij@...ricsson.com, broonie@...nsource.wolfsonmicro.com,
	olalilja@...oo.se, STEricsson_nomadik_linux@...t.st.com, lrg@...com
Subject: Re: [PATCH 5/6] ARM: ux500: Enable HIGHMEM on all mop500 platforms

On 31/07/12 23:01, Russell King - ARM Linux wrote:
> On Tue, Jul 31, 2012 at 08:50:02PM +0000, Arnd Bergmann wrote:
>> On Tuesday 31 July 2012, Russell King - ARM Linux wrote:
>>> I still fail to see how not having highmem enabled would ever cause memory
>>> corruption errors (unless something dealing with memory in a very very
>>> wrong way - iow, not using one of the reservation or memory allocation
>>> methods provided by the kernel.)
>>
>> The problem is that all users of ux500 systems pass a command line like
>>
>> vmalloc=256M mem=128M@0 mali.mali_mem=32M@...M hwmem=168M@...M mem=48M@...M mem_issw=1M@...M mem=640M@...M
>>
>> This is of course totally bogus and should not be done. If I understand
>> Lee correctly, one of the issues resulting from passing a command
>> line like this without enabling highmem is memory corruption.
>
> But the question is _why_ does that corruption happen.
>
>  From the above, we will end up with the kernel getting:
>
> 0x00000000 - 0x07ffffff (128M @ 0)
> 0x14800000 - 0x177fffff (48M  @ 328M)
> 0x18000000 - 0x3fffffff (640M @ 384M)
>
> with:
>
> 0x08000000 - 0x081fffff used for mali
> 0x0a000000 - 0x147fffff used for hwmem
> 0x17f00000 - 0x17ffffff used for mem_issw
>
> Now, with highmem disabled, the kernel should still map exactly the
> regions: 0x00000000 - 0x07ffffff, 0x14800000 - 0x177fffff, into the
> direct mapped region, and truncate the 0x18000000 - 0x3fffffff
> region appropriately, reducing the amount of memory available such
> that it won't overlap the vmalloc area (which you've specified to be
> a minimum of 256M.)
>
> This should _NOT_ cause any memory corruption.
>
> So, come on guys.  Debugging is *mandatory* for this kind of problem.
> Papering over it is obscene.

Actually I didn't go any further with it, as I changed to another 
identical piece of hardware and couldn't reproduce the issue.

FYI, here's the boot log from the broken board:

http://paste.ubuntu.com/1102017/

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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