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

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Date:	Mon, 26 Aug 2013 05:35:53 +0000
From:	Xiubo Li-B47053 <B47053@...escale.com>
To:	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>
CC:	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>,
	"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 Stephen,


> Subject: Re: [PATCH 4/4] Documentation: Add device tree bindings for
> Freescale FTM PWM
> 
> On 08/23/2013 01:36 AM, Thierry Reding wrote:
> > 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).
> 
> I think the pin-muxing should be static, i.e. set up when the PWM device
> as a whole probe()s, rather than being twiddled at request/free time.
> Certainly the pinmux support in the device core is now set up to acquire
> the default state right before probe(). I don't see a need to do anything
> custom here.

As we have tolk about this before in [PATCH 1/4]:
"
> > Why do you need to manipulate the pinctrl to en/disable a channel?
> >
> 
> This is because in Vybrid VF610 TOWER board, there are 4 leds, and each
> led's one point(diode's positive pole) is connected to 3.3V, and the
> other point is connected to pwm's one channel. When the 4 pinctrls are
> configured as enable at the same time, the 4 pinctrls is low valtage, and
> the 4 leds will be lighted up as default, then when you enable/disable
> one led will effects others.
> 
> These pinctrls are belong to pwm, and I don't think led or other customer
> could control them directly.
> So, here I authorize the 4 pinctrls to each channel controls.
>
"
For the reason above, I have to control the pinctrls separately.

If all the pinctrls set as default state, the 8 pinctrls must be controlled together.
And the 4 leds will all be lighted up as default and will influence each other.

Thanks very much.

--
Best Regards.
Xiubo




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