linux-kernel - Re: [PATCH] MXS: Convert mutexes in clock.c to spinlocks

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Message-ID: <20111219032712.GB4962@S2100-06.ap.freescale.net>
Date:	Mon, 19 Dec 2011 11:27:13 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Marek Vasut <marek.vasut@...il.com>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, Wolfgang Denk <wd@...x.de>,
	Stefano Babic <sbabic@...x.de>,
	Shawn Guo <shawn.guo@...aro.org>,
	Huang Shijie <b32955@...escale.com>,
	Sascha Hauer <s.hauer@...gutronix.de>
Subject: Re: [PATCH] MXS: Convert mutexes in clock.c to spinlocks

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.  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?

-- 
Regards,
Shawn

[1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/137282

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