From: linux@arm•linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] MXS: Convert mutexes in clock.c to spinlocks
Date: Mon, 19 Dec 2011 08:22:25 +0000 [thread overview]
Message-ID: <20111219082225.GC14542@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <201112190503.46668.marek.vasut@gmail.com>
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.
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.
next prev parent reply other threads:[~2011-12-19 8:22 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-18 14:06 [PATCH] MXS: Convert mutexes in clock.c to spinlocks Marek Vasut
2011-12-19 3:27 ` Shawn Guo
2011-12-19 4:03 ` Marek Vasut
2011-12-19 8:22 ` Russell King - ARM Linux [this message]
2011-12-19 11:57 ` Marek Vasut
2011-12-19 12:15 ` Russell King - ARM Linux
2011-12-19 20:54 ` Marek Vasut
2011-12-19 21:03 ` Russell King - ARM Linux
2011-12-19 21:05 ` Marek Vasut
2011-12-19 21:28 ` Russell King - ARM Linux
2011-12-19 21:37 ` Marek Vasut
2011-12-19 21:43 ` Marek Vasut
2011-12-19 23:23 ` Shawn Guo
2011-12-19 23:35 ` Marek Vasut
2011-12-20 0:19 ` Shawn Guo
2011-12-20 3:09 ` Marek Vasut
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