linux-kernel - RE: [PATCH 4/4] Documentation: Add device tree bindings for Freescale FTM PWM

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Date:	Mon, 26 Aug 2013 05:46:26 +0000
From:	Xiubo Li-B47053 <B47053@...escale.com>
To:	Thierry Reding <thierry.reding@...il.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Guo Shawn-R65073 <r65073@...escale.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"rob@...dley.net" <rob@...dley.net>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>
Subject: RE: [PATCH 4/4] Documentation: Add device tree bindings for
 Freescale FTM PWM

Hi Thierry,


> Subject: Re: [PATCH 4/4] Documentation: Add device tree bindings for
> Freescale FTM PWM
> 
> On Thu, Aug 22, 2013 at 08:26:10AM +0200, Sascha Hauer wrote:
> > On Thu, Aug 22, 2013 at 02:55:42AM +0000, Xiubo Li-B47053 wrote:
> > > Hi Tomasz,
> > >
> > > Thanks for your comments.
> > >
> > >
> > > > Could you explain meaning of this property more precisely? I'm
> > > > interested especially how is this related to the PWM IP block and
> boards.
> > > >
> > >
> > > Yes.
> > > There are 8 channels most. While the pinctrls of 4th and 5th
> > > channels could be used by uart's Rx and Tx, then these 2 channels
> > > won't be used for pwm output, so there will be 6 channels available
> by the pwm.
> > > Thus, the pwm chip will register only 6 pwms(6 channels)
> > > most("fsl,pwm-channel-orders = {0 1 2 3 6 7}").And also the "fsl,pwm-
> channel-number" will be 6.
> >
> > If the chip has eight PWMs I would register all of them. If some of
> > them are not routed out by the pinmux then just nothing happens if you
> > use them. In a sane devicetree they won't be referenced anyway when
> > they are not routed out of the SoC.
> 
> In that case, shouldn't this be hooked up to the pinctrl subsystem as
> well? As I understand the above, the logical thing would be for each PWM
> channel's .request() operation to configure the pinmuxing appropriately.
> And if it can't be configured as necessary then .request() should return
> an error (or propagate the error from the pinctrl subsystem).
> 

That's maybe better, if so, the pinctrl configuration must be split into two steps:
1, get the channel pinctrl "active" and "idle" states by callig pinctrl_lookup_state() in .request().
2, select the proper state in .enable()/.disable().




Thanks very much.

--
Best Regards.
Xiubo



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