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

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Message-ID: <544509C7.9010309@mleia.com>
Date:	Mon, 20 Oct 2014 16:10:31 +0300
From:	Vladimir Zapolskiy <vz@...ia.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.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 Alexandre,

On 20.10.2014 13:29, Alexandre Belloni wrote:
> 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.

and why do you want to put a thread to sleep in context of the driver?

> I'm not sure why you feel a spinlock would be better here.
> 

Only because a spinlock is lighter than a mutex.

With best wishes,
Vladimir
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