[U-Boot] Cache alignment warnings on Tegra (ARM)

[Simon Glass]

Hi,

On Wed, Sep 12, 2012 at 4:42 PM, Marek Vasut <marex at denx.de> wrote:
> Dear Stephen Warren,
>
>> On 09/12/2012 04:38 PM, Marek Vasut wrote:
>> > Dear Stephen Warren,
>> >
>> >> On 09/12/2012 10:19 AM, Tom Warren wrote:
>> >>> Folks,
>> >>>
>> >>> Stephen Warren has posted an internal bug regarding the cache
>> >>> alignment 'warnings' seen on Tegra20 boards when accessing MMC. Here's
>> >>> the gist:
>> >>>
>> >>> Executing "mmc dev 0" still yields cache warnings:
>> >>>
>> >>> Tegra20 (Harmony) # mmc dev 0
>> >>> ERROR: v7_dcache_inval_range- stop address is not aligned- 0x3fb69908
>> >>> mmc0 is current device
>> >>
>> >> ...
>> >>
>> >>> There have been patches in the past (IIRC) that have tried to ensure
>> >>> all callers (FS, MMC driver, USB driver, etc.) force their buffers to
>> >>> the appropriate alignment, but I don't know that we can ever correct
>> >>> every instance, now or in the future.
>> >>>
>> >>> Can we start a discussion about what we can do about this warning?
>> >>> Adding an appropriate #ifdef (CONFIG_SYS_NO_CACHE_ALIGNMENT_WARNINGS,
>> >>> etc.) where Stephen put his #if 0's would be one approach, or changing
>> >>> the printf() to a debug(), perhaps. As far as I can tell, these
>> >>> alignment 'errors' don't seem to produce bad data in the transfer.
>> >>
>> >> I don't think simply turning off the warning is the correct approach; I
>> >> believe they represent real problems that can in fact cause data
>> >> corruption. I don't believe we have any choice other than to fully solve
>> >> the root-cause.

Yes I agree, and I think it is pretty close - certainly much better
than it used to be. The good thing about them being annoying is that
they will likely get fixed :-)

Regards,
Simon

>> >
>> > Try CONFIG_MMC_BOUNCE_BUFFER or what it was called ... see
>> > inclued/configs/m28evk.h , I use it there.
>>
>> That didn't seem to change anything.
>>
>> I just re-tested and it looks like there's one single instance of this
>> cache warning now when running "mmc dev 0"; there used to be hundreds of
>> them when loading files from eMMC. Perhaps it depends on some runtime
>> allocation or something though, and I'm just getting lucky and seeing
>> fewer of them.
>
> Yes it does, internal unaligned variables passed through to the MMC driver ...
> the bounce buffer should fix that up for you.
>
> Best regards,
> Marek Vasut
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