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

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Date:	Mon, 19 Dec 2011 05:03:45 +0100
From:	Marek Vasut <marek.vasut@...il.com>
To:	Shawn Guo <shawn.guo@...escale.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.

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 ?

M
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