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

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Date:   Wed, 11 Sep 2019 22:25:13 +0200
From:   Andreas Kemnade <andreas@...nade.info>
To:     Dan Murphy <dmurphy@...com>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        <lee.jones@...aro.org>, <jingoohan1@...il.com>,
        <jacek.anaszewski@...il.com>, <pavel@....cz>, <robh+dt@...nel.org>,
        <mark.rutland@....com>, <b.zolnierkie@...sung.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-leds@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-fbdev@...r.kernel.org>,
        "H. Nikolaus Schaller" <hns@...delico.com>
Subject: Re: [PATCH v2 2/2] backlight: lm3630a: add an enable gpio for the
 HWEN pin

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