linux-kernel - Re: [PATCH] lib/atomic64_test: do not build on non-atomic64 systems

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Message-ID: <adavd4ro94d.fsf@cisco.com>
Date:	Sun, 24 Oct 2010 09:20:34 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mike Frysinger <vapier@...too.org>,
	Luca Barbieri <luca@...a-barbieri.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/atomic64_test: do not build on non-atomic64 systems

 > 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?  (I expect x86_64 is probably
OK but I wonder if other architectures might not be so understanding)

 - R.
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