linux-kernel - Re: [PATCH 2/2] gpio: pcf857x: add support for reset-gpios on (most) PCA967x

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Message-ID: <20250220122812.GC20111@pendragon.ideasonboard.com>
Date: Thu, 20 Feb 2025 14:28:12 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Quentin Schulz <quentin.schulz@...rry.de>
Cc: Heiko Stübner <heiko@...ech.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Quentin Schulz <foss+kernel@...il.net>, linux-gpio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] gpio: pcf857x: add support for reset-gpios on (most)
 PCA967x

On Thu, Feb 20, 2025 at 01:13:06PM +0100, Quentin Schulz wrote:
> On 2/20/25 11:52 AM, Heiko Stübner wrote:
> > Am Donnerstag, 20. Februar 2025, 10:56:52 MEZ schrieb Quentin Schulz:
> >> From: Quentin Schulz <quentin.schulz@...rry.de>
> >>
> >> The PCA9670, PCA9671, PCA9672 and PCA9673 all have a RESETN input pin
> >> that is used to reset the I2C GPIO expander.
> >>
> >> One needs to hold this pin low for at least 4us and the reset should be
> >> finished after about 100us according to the datasheet[1]. Once the reset
> >> is done, the "registers and I2C-bus state machine will be held in their
> >> default state until the RESET input is once again HIGH.".
> >>
> >> Because the logic is reset, the latch values eventually provided in the
> >> Device Tree via lines-initial-states property are inapplicable so they
> >> are simply ignored if a reset GPIO is provided.
> >>
> >> [1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 and fig 22.
> >> Signed-off-by: Quentin Schulz <quentin.schulz@...rry.de>
> >> ---
> >>   drivers/gpio/gpio-pcf857x.c | 29 ++++++++++++++++++++++++++---
> >>   1 file changed, 26 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/gpio/gpio-pcf857x.c b/drivers/gpio/gpio-pcf857x.c
> >> index 7c57eaeb0afeba8953d998d8eec60a65b40efb6d..94077208e24ae99a1e8762e783f0eabc580fa520 100644
> >> --- a/drivers/gpio/gpio-pcf857x.c
> >> +++ b/drivers/gpio/gpio-pcf857x.c
> >> @@ -5,6 +5,7 @@
> >>    * Copyright (C) 2007 David Brownell
> >>    */
> >>   
> >> +#include <linux/delay.h>
> >>   #include <linux/gpio/driver.h>
> >>   #include <linux/i2c.h>
> >>   #include <linux/interrupt.h>
> > 
> > this is missing
> > #include <linux/gpio/consumer.h>
> > 
> > because otherwise you end up with
> > ../drivers/gpio/gpio-pcf857x.c: In function ‘pcf857x_probe’:
> > ../drivers/gpio/gpio-pcf857x.c:300:21: error: implicit declaration of function ‘devm_gpiod_get_optional’; did you mean ‘devm_regulator_get_optional’? [-Wimplicit-function-declaration]
> >    300 |         rstn_gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
> >        |                     ^~~~~~~~~~~~~~~~~~~~~~~
> >        |                     devm_regulator_get_optional
> > ../drivers/gpio/gpio-pcf857x.c:300:68: error: ‘GPIOD_OUT_HIGH’ undeclared (first use in this function)
> >    300 |         rstn_gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
> >        |                                                                    ^~~~~~~~~~~~~~
> > ../drivers/gpio/gpio-pcf857x.c:300:68: note: each undeclared identifier is reported only once for each function it appears in
> > ../drivers/gpio/gpio-pcf857x.c:309:17: error: implicit declaration of function ‘gpiod_set_value’ [-Wimplicit-function-declaration]
> >    309 |                 gpiod_set_value(rstn_gpio, 0);
> >        |                 ^~~~~~~~~~~~~~~
> > 
> 
> It compiles just fine on my end, this is all very suspicious.
> 
> GPIO_PCF857X symbol depends on GPIOLIB which builds this function.
> 
> Now, I have no clue how it finds the declaration for me without this 
> include. Any clue?

Possibly indirect includes that depend on your kernel config ? The above
functions and macros are declared and defined in linux/gpio/consumer.h,
so you should include it regardless.

> >> @@ -272,12 +273,11 @@ static const struct irq_chip pcf857x_irq_chip = {
> >>   
> >>   static int pcf857x_probe(struct i2c_client *client)
> >>   {
> >> +	struct gpio_desc *rstn_gpio;

I'd call it reset_gpio as in drivers we deal with logical signals. Up to
you.

> >>   	struct pcf857x *gpio;
> >> -	unsigned int n_latch = 0;
> >> +	unsigned int n_latch;
> >>   	int status;
> >>   
> >> -	device_property_read_u32(&client->dev, "lines-initial-states", &n_latch);
> >> -
> >>   	/* Allocate, initialize, and register this gpio_chip. */
> >>   	gpio = devm_kzalloc(&client->dev, sizeof(*gpio), GFP_KERNEL);
> >>   	if (!gpio)
> >> @@ -297,6 +297,29 @@ static int pcf857x_probe(struct i2c_client *client)
> >>   	gpio->chip.direction_output	= pcf857x_output;
> >>   	gpio->chip.ngpio		= (uintptr_t)i2c_get_match_data(client);
> >>   
> >> +	rstn_gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
> >> +	if (IS_ERR(rstn_gpio)) {
> >> +		return dev_err_probe(&client->dev, PTR_ERR(rstn_gpio),
> >> +				     "failed to get reset GPIO\n");
> >> +	}

No need for curly braces.

> >> +
> >> +	if (rstn_gpio) {
> >> +		/* Reset already held with devm_gpiod_get_optional with GPIOD_OUT_HIGH */
> >> +		usleep_range(4, 8); /* tw(rst) > 4us */
> >> +		gpiod_set_value(rstn_gpio, 0);
> >> +		usleep_range(100, 200); /* trst > 100uS */

Maybe use fsleep() for both ?

> >> +
> >> +		/*
> >> +		 * Reset "will initialize to their default states of all I/Os to
> >> +		 * inputs with weak current source to VDD", which is the same as
> >> +		 * writing 1 for all I/Os which is 0 in n_latch.
> >> +		 */
> >> +		n_latch = 0;
> >> +	} else {
> >> +		device_property_read_u32(&client->dev, "lines-initial-states",
> >> +					 &n_latch);
> > 
> > device_property_read_u32 will not fill n_latch if the property is missing.
> > Before n_latch was always set to 0 at the declaration point above.
> > I guess that should be kept, because we want 0, except if
> > device_property_read_u32 provides a different value.
> 
> Yes, this was an oversight from me, will restore n_latch = 0 at the top 
> of the function. Thanks for catching that.

-- 
Regards,

Laurent Pinchart