linux-kernel - Re: [PATCH] pwm: add support for Intel Low Power Subsystem PWM

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Date:	Wed, 22 Jan 2014 11:31:16 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Chew Chiau Ee <chiau.ee.chew@...el.com>,
	linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chew Kean Ho <kean.ho.chew@...el.com>,
	Chang Rebecca Swee Fun <rebecca.swee.fun.chang@...el.com>
Subject: Re: [PATCH] pwm: add support for Intel Low Power Subsystem PWM

On Tue, Jan 21, 2014 at 08:43:39PM +0100, Thierry Reding wrote:
> The idea behind this is that only a single user can have access to a
> given PWM device at a time. The PWM device's PWMF_REQUESTED flag is set
> (and cleared) under the pwm_lock and any subsequent users will not be
> able to use that specific device (pwm_request() return -EBUSY).
> 
> There is obviously an assumption here that each user knows what they are
> doing and aren't calling any of the public pwm_*() functions
> concurrently. I haven't come across a situation where this is actually a
> problem because typically these functions are called either via sysfs or
> some other higher-level where synchronization is already properly
> handled.
> 
> So the only thing that drivers should be taking care of is synchronizing
> access to registers common to multiple PWM devices.

OK, and since LPSS PWM don't share registers we shouldn't need to do
anything here.

> Does that clarify things?

It does for me, thanks for the explanation.
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