Messages in this thread | | | Date | Wed, 28 Aug 2013 12:33:52 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v4 1/4] lib: Introduce atomic MMIO modify |
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On Wed, 28 Aug 2013 07:24:23 -0300 Ezequiel Garcia <ezequiel.garcia@free-electrons.com> wrote:
> On Tue, Aug 27, 2013 at 01:37:09PM -0700, Andrew Morton wrote: > > On Sat, 24 Aug 2013 12:35:29 -0300 Ezequiel Garcia <ezequiel.garcia@free-electrons.com> wrote: > > > > > Some platforms 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. > > > > Seem sensible. Perhaps. > > > > It only works if both subsystems agree to use atomic_io_modify(). And > > if they're both capable of doing that, they are both capable of > > implementing an agreed-upon internal locking scheme, so why bother? > > > > One of the scenarios where this could be helpful and an agreed-upon > lock seemed difficult to design is this: a watchdog driver that shares > some control register with *two* different clocksource drivers. > > So, one first solution is to have a function in the two clocksource > drivers (with matching prototype) and have the watchdog access > the register through it. > > However, because of multiplatform builds, both these clocksource drivers > could be built at the same time. Therefore we would have a symbol > collision, doubly-defined, in each driver. > > How would that work? What other internal locking scheme could we > implement?
I guess the locking would need to be in a standalone module which the various driver modules would then depend upon. I'm not really advocating doing this - I'm just making noise.
> [..] > > > > I disagree with the presence of the ifndef. If > > __HAVE_ARCH_ATOMIC_IO_MODIFY is undefined, the architecture must still > > implement the identical function signature. The best way to ensure that > > is to use the same prototype in both cases. > > > > I agree, but how can this be done?
Just remove the ifndefs. Then remove the identical function prototype from the arm header.
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