linux-kernel - Re: [PATCH v3 1/2] ASoC: max98927: Handle reset gpio when probing i2c

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Date:   Sat, 04 Sep 2021 01:22:26 +0200
From:   Alejandro Tafalla <atafalla@...on.com>
To:     Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, Takashi Iwai <tiwai@...e.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v3 1/2] ASoC: max98927: Handle reset gpio when probing i2c

On 3/9/21 11:20 Péter Ujfalusi wrote:
> 
> If this is a 'reset' pin then it's ACTIVE state is when it places the
> device to _reset_.
> GPIOD_OUT_LOW == Deasserted state of the GPIO line.
> 
> If the reset pin should be pulled low for reset (GPIO_ACTIVE_LOW) and
> you want the device initially  in reset then you need GPIOD_OUT_HIGH,
> because:
> GPIOD_OUT_HIGH == Asserted state of the GPIO line.
> 
> Same goes for the gpiod_set_value_cansleep():
> 0 - deasserted
> 1 = asserted
> 
> and this all depends on how the gpio is defined in DT
> (GPIO_ACTIVE_LOW/HIGH), which depends on how the documentation refers to
> the pin...
> 
> reset pin:
> low to keep the device in reset, high to release it from reset:
> GPIO_ACTIVE_LOW
> gpiod_set_value_cansleep(0) to enable
> gpiod_set_value_cansleep(1) to disable
> 
> 
> enable pin:
> high to enable the part, low to disable
> GPIO_ACTIVE_HIGH
> gpiod_set_value_cansleep(1) to enable
> gpiod_set_value_cansleep(0) to disable
> 
> In both cases
> electrical 0: reset/disable
> electrical 1: enable
I'll change it to be consistent in the next version. Thank you for the 
explanation.
 
> > +	if (IS_ERR(reset_gpio)) {
> > +		ret = PTR_ERR(reset_gpio);
> > +		return dev_err_probe(&i2c->dev, ret, "failed to request 
GPIO reset
> > pin"); +	}
> > +
> > +	if (reset_gpio) {
> > +		usleep_range(8000, 10000);
> > +		gpiod_set_value_cansleep(reset_gpio, 1);
> > +		usleep_range(1000, 5000);
> > +	}
> > +
> 
> You might want to put the device to reset on remove at minimum.
Okay, thanks.

-- 
Alejandro Tafalla