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From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: "Vokáč Michal" <Michal.Vokac@ysoft.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
	"Lukasz Majewski" <l.majewski@majess.pl>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"Fabio Estevam" <fabio.estevam@nxp.com>,
	"Lothar Waßmann" <LW@karo-electronics.de>
Subject: Re: [RCF PATCH,v2,2/2] pwm: imx: Configure output to GPIO in disabled state
Date: Wed, 14 Nov 2018 10:09:53 +0100	[thread overview]
Message-ID: <20181114090953.jc6wkvgshn32bcm5@pengutronix.de> (raw)
In-Reply-To: <20181109165555.vqbiwh4hlcnozdna@pengutronix.de>

Hello Michal,

On Fri, Nov 09, 2018 at 05:55:55PM +0100, Uwe Kleine-König wrote:
> On Fri, Nov 09, 2018 at 02:24:42PM +0000, Vokáč Michal wrote:
> > On 8.11.2018 20:18, Uwe Kleine-König wrote:
> > > On Thu, Nov 08, 2018 at 03:21:44PM +0000, Vokáč Michal wrote:
> > >> Hi Uwe,
> > >>
> > >> On 7.11.2018 16:01, Uwe Kleine-König wrote:
> > >>>> Interesting idea. I just wonder why nobody else did not come up with such
> > >>>> a simple solution before.
> > >>>
> > >>> I think I mentioned it already in this thread, but it went unnoticed :-)
> > >>
> > >> I meant it like "How happened this was not invented years ago, when people
> > >> first noticed the issue with using inverted PWM for backlight on i.MX6."
> > >> In our project, this issue dates back to 2015 :(
> > >>
> > >>> Then the patch isn't correct yet. The idea is always keep the hardware
> > >>> running and only disable it if it's uninverted.
> > >>
> > >> OK, I got the point.
> > >>
> > >>> In imx_pwm_probe it's not yet known what the polarity is supposed to be,
> > >>> right?
> > >>
> > >> Not really. It can already be known but currently there is no way how to
> > >> pass the information to the probe function. I, as a creator of the device
> > >> (and author of a DTS file) know that the circuit needs inverted PWM signal.
> > >> And I know that the circuit needs to be disabled until I say it can be
> > >> enabled. How I say that can warry. It may be default brightness level > 0
> > >> in DTS file or from a userspace program using PWM sysfs interface.
> > >>
> > >>>   So the right thing to do there is to not touch the configuration
> > >>> of the pwm. I think all states that are problematic then are also
> > >>> problematic with the gpio/pinmux approach.
> > >>
> > >> I think my use-case I already presented before is an example where
> > >> involving pinctrl solves the problem while the "leave PWM enabled
> > >> for inverted users" does not. That is all the time between
> > >> imx_pwm_probe() and imx_pwm_apply_v2().
> > > 
> > > You're doing in probe:
> > > 
> > >    if (pwm_is_running()):
> > >      mux(pin, function=pwm)
> > >    else:
> > >      gpio_set_value(gpio, 0)
> > >      mux(pin, function=gpio)
> > > 
> > > This gives you the right level assuming the gpio specification uses the
> > > right flag (GPIO_ACTIVE_HIGH or GPIO_ACTIVE_LOW).
> > 
> > Agree.
> > 
> > > Taking your example with the backlight device you specify an "init" and
> > > a "default" pinctrl and only "default" contains the muxing for the PWM
> > > pin everything should be as smooth as necessary: The pwm is only muxed
> > > when the backlight device is successfully bound.
> > 
> > Have you tried that Uwe? The bad news is I tested that before and now
> > again and it does not work like that. We already discussed that earlier.
> 
> The key is that the pinmux setting for the PWM pin should be part of the
> bl pinctrl, not the pwm pinctrl. Then "default" is only setup when the
> bl device is successfully bound which is after the bl's .probe callback
> called pwm_apply().

Did my mail clear up my suggestion? Do you agree it should work like
this (or even did you test that, as I did not)?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

  reply	other threads:[~2018-11-14  9:10 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-10  9:33 [RCF PATCH v2 0/2] pwm: imx: Configure output to GPIO in disabled state Vokáč Michal
2018-10-10  9:33 ` [RCF PATCH v2 1/2] dt-bindings: pwm: imx: Allow switching PWM output between PWM and GPIO Vokáč Michal
2018-10-10 13:39   ` Thierry Reding
2018-10-29 15:52     ` Vokáč Michal
2018-10-10  9:33 ` [RCF PATCH v2 2/2] pwm: imx: Configure output to GPIO in disabled state Vokáč Michal
2018-10-12  8:57   ` [RCF PATCH,v2,2/2] " Uwe Kleine-König
2018-10-12 15:04     ` Vokáč Michal
2018-10-12 15:54       ` Thierry Reding
2018-10-12 16:08       ` Uwe Kleine-König
2018-10-14 20:24         ` Uwe Kleine-König
2018-10-15  8:45           ` Thierry Reding
2018-10-29 15:55             ` Vokáč Michal
2018-10-29 15:54         ` Vokáč Michal
2018-11-07  9:33           ` Uwe Kleine-König
2018-11-07 13:32             ` Vokáč Michal
2018-11-07 15:01               ` Uwe Kleine-König
2018-11-08 15:21                 ` Vokáč Michal
2018-11-08 19:18                   ` Uwe Kleine-König
2018-11-09 14:24                     ` Vokáč Michal
2018-11-09 16:55                       ` Uwe Kleine-König
2018-11-14  9:09                         ` Uwe Kleine-König [this message]
2018-11-14 11:34                         ` Thierry Reding
2018-11-14 21:51                           ` Uwe Kleine-König
2018-11-15 15:25                             ` Thierry Reding
2018-11-15 20:37                               ` Uwe Kleine-König
2018-11-16  7:34                                 ` Lothar Waßmann
2018-11-16  8:25                                   ` Uwe Kleine-König
2018-11-22 15:42                                     ` Vokáč Michal
2018-11-22 16:23                                       ` Uwe Kleine-König
2018-11-22 16:46                                         ` Vokáč Michal
2018-11-22 19:03                                           ` Uwe Kleine-König
2018-11-23 15:15                                             ` Vokáč Michal
2018-11-25 20:56                                               ` Uwe Kleine-König
2018-11-26  9:11                                                 ` Lothar Waßmann
2018-11-26  9:18                                                   ` Uwe Kleine-König
2018-11-26 10:03                                                     ` Lothar Waßmann
2018-11-26 11:51                                               ` Thierry Reding
2018-11-26 12:23                                                 ` Lothar Waßmann
2018-11-26 13:34                                                   ` Thierry Reding
2018-11-26 15:50                                                     ` Vokáč Michal
2018-11-16  9:51                                 ` Thierry Reding
2018-11-16 10:39                                   ` Uwe Kleine-König
2018-11-16 11:56                                     ` Lothar Waßmann
2018-11-18 11:30                                       ` Uwe Kleine-König
2018-11-16 12:24                                     ` Thierry Reding
2018-11-18 20:08                                       ` Uwe Kleine-König
2018-11-19  8:48                                         ` Uwe Kleine-König
2018-11-22 15:03                                         ` Thierry Reding
2018-11-22 16:17                                           ` Uwe Kleine-König
2018-11-20 13:14                                   ` Vokáč Michal
2018-11-20 16:54                                     ` Uwe Kleine-König
2018-11-22 14:23                                       ` Vokáč Michal
2018-11-19  7:44                             ` Linus Walleij
2018-11-19  8:32                               ` Uwe Kleine-König
2018-11-20  8:35                                 ` Linus Walleij
2018-11-20  9:16                                   ` Viresh Kumar
2018-11-20  9:53                                   ` Uwe Kleine-König
2018-11-14 11:14                   ` Thierry Reding
2018-10-12 16:00   ` [RCF PATCH v2 2/2] " Thierry Reding
2018-10-29 15:53     ` Vokáč Michal

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