[U-Boot] [RFC PATCH v2] ARM: Avoid compiler optimization for usages of readb, writeb and friends.

[Albert ARIBAUD]

Le 19/12/2010 11:22, Alexander Holler a écrit :
> Hello,
>
> On 19.12.2010 08:51, Dirk Behme wrote:
>> On 18.12.2010 23:27, Alexander Holler wrote:
>>> gcc 4.5.1 seems to ignore (at least some) volatile definitions,
>>> avoid that as done in the kernel.
>>>
>
>> Acked-by: Dirk Behme<dirk.behme at googlemail.com>
>
> Thanks for the ack, but I have to say, that those barriers are having
> side effects here. Reading NAND now fails on my BeagleBoard. Regardless
> if I use gcc 4.3.5 or gcc 4.5.1, after applying that patch the wrong ID
> of the NAND is read. In nand_get_flash_type()
> (drivers/mtd/nand/nand_base.c) without that patch I will get the following:
>
> *maf_id: 44, dev_id: 186
>
> with the patch the following is read:
>
> *maf_id: 128, dev_id: 85
>
> Which just is wrong.
>
> I haven't looked further up to now, maybe thats just a side effect of
> some wrong clock settings because of different timings through those
> barrieres or whatever.

IIUC, the patch is adding barriers to every HW register write and read, 
which makes the compiler stop reordering these, and keep them ordered as 
in the source code. Are you sure that the order as laid out in the 
source is the right one? Maybe you were just luck so far that the 
reordering masked a bug.

Amicalement,
-- 
Albert.