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

Albert ARIBAUD
2010-12-22T07:02:25Z

Le 22/12/2010 01:11, Alexander Holler a ?crit :
> 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.

Yes, and this is enough for me to not want it right away: we caught this
one, but how many others, so far unseen, will creep up?

> 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).

Do we need hard floating point in u-boot? IIRC, and unless this changed,
the kernel does not want floating point, so I wonder why u-boot would.

As for getting 4.5 to work, for the next cycle people can still use pre
4.5 gccs / toolchains, so this is important but not urgent to the point
of rushing decisions.

> Regards,
>
> Alexander

Amicalement,
--
Albert.