[U-Boot] [PATCH] arm: enable unaligned access on ARMv7

Aneesh V
2012-06-25T21:49:27Z

Hi Albert,

On 06/25/2012 01:34 PM, Albert ARIBAUD wrote:
> Hi Aneesh,
>
>>>> BTW, I agree that enabling un-aligned access is not a bad idea.
>>>
>>> Just being "not a bad idea" is not enough for me to accept this. It
>>> will have to be the sole sound solution to a problem, and at this
>>> point, I do not think it is as far as USB structure mis-alignement
>>> issues are concerned.
>>
>> My point is that enabling un-aligned accesses in itsown merit
>> is not a bad idea, not as a solution to this problem. I have seen
>> it being enabled in HLOS environment. TI's Symbian port for
>> instance had it enabled for OMAP3. I don't
>> know why Linux too shoudln't take advantage of such hw
>> features. Perhaps you don't want to take it at this point of time to
>> force the real solution to the USB problem, which is reasonable.
>
> What is the (non-contrived) problem to which allowing mis-aligned
> accesses would be a solution?

memcpy() when there is a mismatch in the alignment of source and
destination buffers. Let's say the source buffer is 4 byte aligned
but the destination buffer is only 2 byte aligned. I believe relaxed
alignment requirements will help in writing an accelerated memcpy
routine for this case.

Again, my point is that as a platform software provider I would like
to enable such features to make maximum things work on my platform,
where as the developer of a generic sw module should probably avoid
depending on such features to ensure maximum portability.

br,
Aneesh