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    SubjectRe: [PATCH] MXS: Convert mutexes in clock.c to spinlocks
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    > On Mon, Dec 19, 2011 at 05:03:45AM +0100, Marek Vasut wrote:
    > > > On Sun, Dec 18, 2011 at 03:06:13PM +0100, Marek Vasut wrote:
    > > > > The mutexes can't be safely used under certain circumstances. I
    > > > > noticed this
    > > >
    > > > > issue during some network instability at home:
    > > > Yes, this is a known issue. And there was some discussion[1] about
    > > > why mutex is needed.
    > >
    > > Thanks for pointing this out, I was unaware of it.
    > >
    > > > But I really have not thought about why we can
    > > > not use spinlock only, since using mutex only leads to the issue we
    > > > are seeing here, and using spinlock in enable/disable and mutex in
    > > > rate/parent will not work, because the mxs clocks have enable/disable
    > > > and rate/parent functions access the same register. I know it's not
    > > > good to hold spinlock in rate/parent functions for a long time, but
    > > > do we have a way around rather than using spinlock for both sets of
    > > > functions?
    > >
    > > Yea, spinlock is not good either. On the other hand, is it really held
    > > for so long ?
    >
    > There is another solution to this, which I've pointed out before when
    > this has come up:
    >
    > 1. Convert all your drivers to _also_ use clk_prepare()/clk_unprepare().
    > You need to do this anyway as it will become mandatory for the common
    > clk stuff.
    >
    > 2. Rename your existing clk_enable()/clk_disable() implementation to
    > clk_prepare()/clk_unprepare(). Ensure CONFIG_HAVE_CLK_PREPARE is
    > selected.
    >
    > 3. Provide a new no-op clk_enable()/clk_disable() functions.

    Well, I'm still unsure how'd you then enable/disable the clock ?
    clk_prepare/clk_unprepare is good, but how would that help in avoiding the
    mutex/spinlock?

    >
    > This fixes the issue because clk_prepare()/clk_unprepare() must only be
    > called from process contexts, whereas clk_enable()/clk_disable() may be
    > called from atomic contexts as well.

    Sure, but I need to enable the clock in atomic context ...

    M


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