Re: [Xenomai-core] [Patch 4/7] Define ARM atomic operations in user-space

[Philippe Gerum <rpm@xenomai.org>]

Gilles Chanteperdrix wrote:
> On Sat, May 3, 2008 at 12:34 AM, Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org> wrote:
>>  The include/asm-arm/atomic.h header now defines the xnarch_memory_barrier in
>>  addition to user-space atomic operations. The pxa3xx deserves a special
>>  treatment since it uses the ARMv6 memory barrier operation whereas being an
>>  ARMv5 for other operations, hence a special --enable-arm-mach=pxa3xx option in
>>  configure.in.
> 
> After a quick look at all architectures xenomai supports, it seems
> that we can implement atomic_cmpxchg for most of them in user-space.
> The only one for which I have a doubt is blackfin. Since linux for
> blackfin is uclinux, can we call cli/sti from user-space ?
> 

Nope, these are supervisor's toys on this arch. IIRC, recent Blackfin releases
should be providing fast atomic ops from userland despite this, by using
protected jumps to kernel space for that purpose. I need to check that in the
kernel code, this was a discussion running on the Blackfin dev-list months ago.
Anyway, I would suggest to exclude Blackfin from the mutex optimization set
right now, then go back to it when we support their latest kernel.

-- 
Philippe.