Re: [PATCH v2 2/2] backlight: lm3630a: add an enable gpio for the HWEN pin

From: Andreas Kemnade <andreas@kemnade.info>
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>
Subject: Re: [PATCH v2 2/2] backlight: lm3630a: add an enable gpio for the HWEN pin
Date: Wed, 11 Sep 2019 22:25:13 +0200	[thread overview]
Message-ID: <20190911222513.489b5235@aktux> (raw)
In-Reply-To: <a3f10318-11f4-3b78-47e5-d9add8a46791@ti.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