lkml.org 
[lkml]   [2010]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] lib/atomic64_test: do not build on non-atomic64 systems
On Sun, 24 Oct 2010 09:20:34 -0700 Roland Dreier <rdreier@cisco.com> wrote:

> > That's only part of the problem. The following won't build also:
>
> > drivers/infiniband/hw
>
> Interesting... I hadn't looked at that usage before. Both drivers that
> seem to use atomic64 already depend on 64BIT in Kconfig, so I suspect
> the intersection of 64BIT and !ATOMIC64 is empty?
>
> But eg drivers/infiniband/hw/qib/qib_rc.c does essentially:
>
> atomic64_t *maddr;
> u64 sdata = <something>
> ...
> maddr = (atomic64_t *) qp->r_sge.sge.vaddr;
> atomic64_add_return(sdata, maddr)
>
> is it legit to cast some random address to atomic64_t and expect it to
> work across archs that implement atomic64?

Not really. If someone implements atomic64 on 32-bit they may
do it by putting a spinlock in the atomic64_t. Or they might use
hashed spinlocks, in which case that'll work.

Probably hashed spinlocks, given the (realtively new) convention that
the all-zeroes pattern is a legit way of initialising an atomic_t.



\
 
 \ /
  Last update: 2010-10-25 03:55    [W:0.060 / U:0.228 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site