linux-kernel - Re: [PATCHv8 1/2] pwm: Add Allwinner SoC support

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Date:	Mon, 20 Oct 2014 12:29:39 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Vladimir Zapolskiy <vz@...ia.com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	jonsmirl@...il.com, Simon <longsleep@...il.com>,
	linux-pwm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv8 1/2] pwm: Add Allwinner SoC support

Hi,

On 20/10/2014 at 00:22:57 +0300, Vladimir Zapolskiy wrote :
> > +struct sun4i_pwm_chip {
> > +	struct pwm_chip chip;
> > +	struct clk *clk;
> > +	void __iomem *base;
> > +	struct mutex ctrl_lock;
> 
> why do you use mutex? I haven't found any blocking subcalls under
> protection, a spinlock seems to fit better here.
> 

A mutex here will do the right thing. The lock is never taken in
interrupt context and a mutex is spinning for a few cycles before
putting the thread to sleep. I'm not sure why you feel a spinlock would
be better here.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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