[PATCH v3 1/3] ARM: Introduce atomic MMIO modify
Catalin Marinas
catalin.marinas at arm.com
Fri Aug 23 07:48:05 EDT 2013
On Fri, Aug 23, 2013 at 12:32:26PM +0100, Ezequiel Garcia wrote:
> On Fri, Aug 23, 2013 at 08:07:50AM -0300, Ezequiel Garcia wrote:
> > On Fri, Aug 23, 2013 at 01:38:02PM +0300, Baruch Siach wrote:
> > > On Fri, Aug 23, 2013 at 07:24:03AM -0300, Ezequiel Garcia wrote:
> > > > Some SoC have MMIO regions that are shared across orthogonal
> > > > subsystems. This commit implements a possible solution for the
> > > > thread-safe access of such regions through a spinlock-protected API.
> > > >
> > > > Concurrent access is protected with a single spinlock for the
> > > > entire MMIO address space. While this protects shared-registers,
> > > > it also serializes access to unrelated/unshared registers.
> > > >
> > > > We add relaxed and non-relaxed variants, by using writel_relaxed and writel,
> > > > respectively. The rationale for this is that some users may not require
> > > > register write completion but only thread-safe access to a register.
> > > >
> > > > Signed-off-by: Ezequiel Garcia <ezequiel.garcia at free-electrons.com>
> > >
> > > Is there a reason why this should be limited to ARM? I haven't found anything
> > > ARM specific in the code.
> >
> > I guess not.
>
> ... or maybe yes. I'm not seeing {readl,writel}_relaxed as guaranteed
> to exist in every architecture. So, indeed, this seems to be ARM-dependent.
There was a discussion couple of years ago to make these part of the IO
specification since many architectures define them:
http://thread.gmane.org/gmane.linux.ports.arm.kernel/117626
(and some older threads on linux-arch which I haven't searched)
We could have some default implementation pointing to readl/writel while
letting the arch code to define more optimised variants.
--
Catalin
More information about the linux-arm-kernel
mailing list