linux-kernel - Re: cmpxchg is not available to generic code

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Message-Id: <20070719.002716.30181989.davem@davemloft.net>
Date:	Thu, 19 Jul 2007 00:27:16 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	akpm@...ux-foundation.org
Cc:	airlied@...ux.ie, linux-kernel@...r.kernel.org
Subject: Re: cmpxchg is not available to generic code

From: Andrew Morton <akpm@...ux-foundation.org>
Date: Thu, 19 Jul 2007 00:05:49 -0700

> What's that code doing anyway?  driver-private locking primitives?

It's an atomic lock shared with userspace.  Whatever implementation is
used to do the lock on that object must be identical in the userspace
DRM bits.

Unlike futex, the lock operation on the user side isn't optional.
So if the platform can't do a true cmpxchg it generally cannot
support DRM.

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