linux-kernel - Re: [PATCH v2] pwm-backlight: fix the panel power sequence

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Date:	Fri, 30 Oct 2015 15:41:40 +0800
From:	YH Huang <yh.huang@...iatek.com>
To:	Philipp Zabel <p.zabel@...gutronix.de>
CC:	Thierry Reding <thierry.reding@...il.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	<linux-pwm@...r.kernel.org>, <linux-fbdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	<linux-mediatek@...ts.infradead.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	<yingjoe.chen@...iatek.com>,
	"Jean-Christophe Plagniol-Villard" <plagnioj@...osoft.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] pwm-backlight: fix the panel power sequence

Hi Hpilipp,

On Thu, 2015-10-29 at 16:40 +0100, Philipp Zabel wrote:
> Hi YH,
> 
> Am Donnerstag, den 22.10.2015, 23:12 +0800 schrieb YH Huang:
> > In the case of the panel disabled by the bootloader,
> > your patch still has the following code and always enables the backlight
> > in the probe function.
> > pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
> > -						  GPIOD_OUT_HIGH);
> 
> You are right.
> 
> > What do you think if I remove these two lines in my patch?
> > if (pb->enable_gpio)
> > 	gpiod_direction_output(pb->enable_gpio, 0);
> 
> That won't work if the gpio is still configured as input. How about I
> add the GPIOD_ASIS change to my patch you remove that and the above from
> yours?

I revise these two lines 
if (pb->enable_gpio)
	gpiod_direction_output(pb->enable_gpio, 0);
into
if (pb->enable_gpio) {
	if(gpiod_get_value(pb->enable_gpio) == 0)
		gpiod_direction_output(pb->enable_gpio, 0);
	else
		gpiod_direction_output(pb->enable_gpio, 1);
}

I am not sure what "phandle" is working for.
My change is like your patch but remove the "phandle related" and
"gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT".
Do we really need these?

Also, do you think it is right that I do the "pwm_enable(pb->pwm);"
before "gpiod_set_value(pb->enable_gpio, 1);" in power on function?

Regards,
YH Huang

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