[PATCH v3] arm64: enable EDAC on arm64

[Rob Herring]

On Tue, Apr 22, 2014 at 5:24 AM, Will Deacon <will.deacon at arm.com> wrote:
> Hi Rob,
>
> On Mon, Apr 21, 2014 at 05:09:16PM +0100, Rob Herring wrote:
>> From: Rob Herring <robh at kernel.org>
>>
>> Implement atomic_scrub and enable EDAC for arm64.
>>
>> Signed-off-by: Rob Herring <robh at kernel.org>
>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>> Cc: Will Deacon <will.deacon at arm.com>
>
> [...]
>
>> diff --git a/arch/arm64/include/asm/edac.h b/arch/arm64/include/asm/edac.h
>> new file mode 100644
>> index 0000000..8a3d176
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/edac.h
>> @@ -0,0 +1,38 @@
>> +/*
>> + * Copyright 2013 Calxeda, Inc.
>> + * Based on PPC version Copyright 2007 MontaVista Software, Inc.
>> + *
>> + * This program is free software; you can redistribute it and/or modify it
>> + * under the terms and conditions of the GNU General Public License,
>> + * version 2, as published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope it will be useful, but WITHOUT
>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
>> + * more details.
>> + */
>> +#ifndef ASM_EDAC_H
>> +#define ASM_EDAC_H
>> +/*
>> + * ECC atomic, DMA, SMP and interrupt safe scrub function.
>
> What do you mean by `DMA safe'? For coherent (cacheable) DMA buffers, this
> should work fine, but for non-coherent (and potentially non-cacheable)
> buffers, I think we'll have problems both due to the lack of guaranteed
> exclusive monitor support and also eviction of dirty lines.

That's just copied from other implementations. I agree you could have
a problem here although I don't see why dirty line eviction would be.
There's not really a solution other than not doing s/w scrubbing or
doing it in h/w. So it is up to individual drivers to decide what to
do, but we have to provide this function just to enable EDAC.

Rob

>
> Will
>
>> + * Implements the per arch atomic_scrub() that EDAC use for software
>> + * ECC scrubbing.  It reads memory and then writes back the original
>> + * value, allowing the hardware to detect and correct memory errors.
>> + */
>> +static inline void atomic_scrub(void *va, u32 size)
>> +{
>> +     unsigned int *virt_addr = va;
>> +     unsigned int i;
>> +
>> +     for (i = 0; i < size / sizeof(*virt_addr); i++, virt_addr++) {
>> +             long result;
>> +             unsigned long tmp;
>> +
>> +             asm volatile("/* atomic_scrub */\n"
>> +             "1:     ldxr    %w0, %2\n"
>> +             "       stxr    %w1, %w0, %2\n"
>> +             "       cbnz    %w1, 1b"
>> +                     : "=&r" (result), "=&r" (tmp), "+Q" (*virt_addr) : : );
>> +     }
>> +}
>> +#endif
>> --
>> 1.9.1
>>
>>