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

[Alexander Holler]

Am 21.12.2010 21:04, schrieb Dirk Behme:
> On 21.12.2010 20:52, Wolfgang Denk wrote:
>> Dear Albert&   friends,
>>
>> what is your opinion?  Should we include the memory barrier patch into
>> the upcoming release (and eventually delay it for further testing), or
>> release as is and solve this issue in the next release?
>>
>> I tend to leave it as is, as I expect that most people will disappear
>> in the next few days for holidays, so no much testing will be done
>> anyway, and we then can solve this with less pressure in the next
>> release - but I'm not really sure if this is a good idea?
>
> I somehow tend to leave it as is, too.
>
> We have issues with some recent compilers. For these we found a fix
> using the io.h somehow the same way the Linux kernel does. But this
> introduces new issues for us, we haven't found a proper fix yet
> (except changing the code to the 'old' io.h style). But we don't know
> where we might have this issue additionally, yet.

The only real problem found with that patch was one with a register 
which doesn't like an (unmotivated) read after write.

On the other side, without that patch, using gcc >= 4.5.x (at least on 
arm) proved to fail. In contrast to that problem of gcc 4.5.x ignoring 
that volatile, 4.5.x still fixes many bugs for arm and gcc >= 4.5.x is 
necessary for hardfloat. So it's likely that more people will start 
using 4.5.x (4.5.2 was just released).

Regards,

Alexander