From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lothar =?UTF-8?B?V2HDn21hbm4=?= <LW@KARO-electronics.de>
Subject: Re: [PATCH v3] pwm: imx: Let PWM be active during suspend
Date: Mon, 11 Dec 2017 16:55:45 +0100
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To: Fabio Estevam <festevam@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>, linux-pwm@vger.kernel.org, Rob Herring <robh@kernel.org>, Russell King <linux@arm.linux.org.uk>, Fabio Estevam <fabio.estevam@nxp.com>, Lukasz Majewski <lukma@denx.de>

Hi,

On Mon, 11 Dec 2017 13:07:46 -0200 Fabio Estevam wrote:
> Hi Lothar,
> 
> On Mon, Dec 11, 2017 at 11:20 AM, Lothar Waßmann <LW@karo-electronics.de> wrote:
> 
> > The problem is, that the PWM output goes low whenever the PWM is
> > disabled, no matter what polarity is programmed. So, you would need to
> > prevent the PWM from being disabled whenever the duty cycle is set to 0.
> 
> Yes, that's the key point: PWM output goes low when PWM is disabled.
> 
> I don't think we can workaround this behaviour in the pwm-imx driver.
> 
> So at the moment I see two ways to fix this:
> 
> 1. Set the STOPEN bit which is what I do in this patch
> 
This should probably work.
But this won't fix the issue, that the LED or backlight is turned fully
on when the brightness value is set to 0, since both the leds-pwm and
the pwmbl driver explicitly disable the PWM, when the brightness
value is set to 0.

> 2. Add support for allowing changing pinctrl in suspend:
> https://pastebin.com/71UGrnkA
> 
> This way we can configure the pwm output pin as Hi-Z during suspend.
> 
> What do you think?
>
It would be better to enable the 22K pullup on the pin. Otherwise the
pin will be floating when there is no external pullup resistor.


Lothar Waßmann