[PATCH 3/4] ARM: mm: kill unused TLB_CAN_READ_FROM_L1_CACHE and use ALT_SMP instead

From: gregory.clement@free-electrons.com (Gregory CLEMENT)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 3/4] ARM: mm: kill unused TLB_CAN_READ_FROM_L1_CACHE and use ALT_SMP instead
Date: Wed, 15 May 2013 16:46:20 +0200	[thread overview]
Message-ID: <51939FBC.3060705@free-electrons.com> (raw)
In-Reply-To: <20130515140607.GI23869@mudshark.cambridge.arm.com>

On 05/15/2013 04:06 PM, Will Deacon wrote:
> On Wed, May 15, 2013 at 02:54:14PM +0100, Gregory CLEMENT wrote:
>> On 05/15/2013 03:41 PM, Will Deacon wrote:
>>> Is this using dmatest.ko, or a different test program?
>>
>> No they are self-test from the mv_xor driver
> 
> Ok. And the CPU locks up, rather than the DMA master?
> 
>>> Ok, so the ALT_UP case should be emitted after patching, correct?
>>
>> Indeed it was I excepted but I didn't check (I don't know how to do)
> 
> If you don't have JTAG, that's trickier. Hopefully my other suggestion will
> help.
> 
>>>> I made some investigation. And in UP if I remove the line:
>>>> 	ALT_UP(W(nop))
>>>
>>> Did you remove the ALT_SMP case as well? You could also try making the
>>> ALT_SMP case use W(nop) too and see if it changes anything.
>>
>> OK I will try it.
> 
> You could also try deleting both of the ALT_* lines and just putting a
> W(nop) in there directly.

If I just delete the both of the ALT_* lines it no more hangs.
If I put a  W(nop) instead it hangs.

> 
>>> If you don't have both of the alternatives, things will go wrong.
>>
>> For my own culture, how ALT_UP and ALT_SMP work in SMP case?
>> When I disassembled the proc-v7.o, I saw that the SMP variant of the code were
>> written. How the kernel switch to the UP version of the code?
> 
> Early in boot (head.S:__fixup_smp), we detect whether the CPU has the MP
> extensions then, if we're actually UP but the kernel has CONFIG_SMP=y, we
> walk over the .alt.smp.init section looking at each entry in there. The
> ALT_UP macro spits out an (address, instruction) pair, so in
> __do_fixup_smp_on_up, we store the instruction to the address for each pair,
> replacing the SMP instruction which sat there in the compiled image.
> 
> It could be that the CPUID checks are failing on your Marvell part. Can you
> tell me what you have in your mpidr (mrc p15, 0, Rd, c0, c0, 5) and also
> your midr (mrc p15, 0, Rd, c0, c0) please?

mpidr= 0x0
midr= 0x561F5811

> 
> Cheers,
> 
> Will
> 
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-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com