From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andreas Kemnade <andreas@kemnade.info>
Date: Wed, 11 Sep 2019 20:25:13 +0000
Subject: Re: [PATCH v2 2/2] backlight: lm3630a: add an enable gpio for the HWEN pin
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        <a3f10318-11f4-3b78-47e5-d9add8a46791@ti.com>
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To: Dan Murphy <dmurphy@ti.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>, lee.jones@linaro.org, jingoohan1@gmail.com, jacek.anaszewski@gmail.com, pavel@ucw.cz, robh+dt@kernel.org, mark.rutland@arm.com, b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-leds@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fbdev@vger.kernel.org, "H. Nikolaus Schaller" <hns@goldelico.com>

On Wed, 11 Sep 2019 13:48:36 -0500
Dan Murphy <dmurphy@ti.com> wrote:


> >> @@ -535,6 +538,13 @@ static int lm3630a_probe(struct i2c_client *client,
> >>   	}
> >>   	pchip->pdata = pdata;
> >>   
> >> +	pchip->enable_gpio = devm_gpiod_get_optional(&client->dev, "enable",
> >> +						GPIOD_OUT_HIGH);
> >> +	if (IS_ERR(pchip->enable_gpio)) {
> >> +		rval = PTR_ERR(pchip->enable_gpio);
> >> +		return rval;  
> 
> the enable gpio is optional so if it fails you log the error and move on
>
well, if the gpio is not there, then it returns NULL.
It might return e.g. -EDEFER. So I need to check for errors here.
 
> Also on driver removal did you want to set the GPIO to low to disable 
> the device to save power?
> 
page 5 of the datasheet says:

Ishdn = Typ. 1µA max. 4µA.
For HWEN=Vin, I2c shutdown  (I guess this means outputs powered off)
ond for HWEN=GND.

So are we really saving something here?

Regards,
Andreas