Re: [RFT] [SPARC] Emulate cmpxchg like parisc

[David Miller <davem@davemloft.net>]

From: Dave Airlie <airlied@linux.ie>
Date: Sat, 26 May 2007 21:32:10 +0100 (IST)

> the DRM can use cmpxchg in userspace, to implement DRM_CAS, have a look in 
> drm git libdrm/xf86drm.h we appear to have a sparc implementation, this 
> gives us fast userspace locking, however if an arch doesn't implement 
> DRM_CAS we fallback to the heavyweight in-kernel lock,

That instruction only works on sparc64 cpus, which includes
32-bit apps running a system with sparc64 cpus.

That's why I hard-code the opcode in that asm statement of
the DRM sources.