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

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Date:	Tue, 18 Feb 2014 12:05:35 +0000
From:	"Chew, Chiau Ee" <chiau.ee.chew@...el.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Thierry Reding <thierry.reding@...il.com>
CC:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	"linux-kernel@...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>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: RE: [PATCH] pwm: add support for Intel Low Power Subsystem PWM

> -----Original Message-----
> From: Mika Westerberg [mailto:mika.westerberg@...ux.intel.com]
> Sent: Wednesday, January 22, 2014 5:31 PM
> To: Thierry Reding
> Cc: One Thousand Gnomes; Chew, Chiau Ee; linux-pwm@...r.kernel.org; linux-
> kernel@...r.kernel.org; Chew, Kean Ho; Chang, Rebecca Swee Fun
> 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.

Hi Thierry,

Would like to find out whether this pwm patch ready to get accepted into mainline kernel? Didn't mean to be pushy :).
Btw, in order to have the Intel Baytrail PWM controller working, it has dependency on the acpi_lpss.c which I have sent the patch (https://lkml.org/lkml/2014/2/18/127) for upstream as well and cc you in the loop. 

Thanks,
Chiau Ee
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