linux-kernel - Re: [PATCH 4/9] gpio: regmap: add the .get

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Message-ID: <sbvgkepshytjklww6ifttbeg5zg6szlp43qsi75zwkstcgffqv@gritt6czkkej>
Date: Mon, 14 Jul 2025 16:17:58 +0300
From: Ioana Ciornei <ioana.ciornei@....com>
To: Michael Walle <mwalle@...nel.org>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Linus Walleij <linus.walleij@...aro.org>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Shawn Guo <shawnguo@...nel.org>, Lee Jones <lee@...nel.org>, 
	Frank Li <Frank.Li@....com>
Subject: Re: [PATCH 4/9] gpio: regmap: add the .get_direction() callback

On Wed, Jul 09, 2025 at 05:01:38PM +0200, Michael Walle wrote:
> Hi Ioana,
> 
> great to see another user of gpio-regmap.
> 
> On Wed Jul 9, 2025 at 1:26 PM CEST, Ioana Ciornei wrote:
> > There are GPIO controllers such as the one present in the LX2160ARDB
> > QIXIS CPLD which are single register fixed-direction. This cannot be
> > modeled using the gpio-regmap as-is since there is no way to
> > present the true direction of a GPIO line.
> 
> You mean input and output mixed together in one register? At least
> to me, that wasn't so obvious by the commit message, I had to look
> at the actual driver.
> 

Yes, that is right. I will update the commit message to make it more
clear for everybody.

> > In order to make this use case possible, add a new callback to the
> > gpio_config structure - .get_direction() - which can be used by user
> > drivers to provide the fixed direction per GPIO line.
> >
> > Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
> > ---
> >  drivers/gpio/gpio-regmap.c  | 17 ++++++++++++++++-
> >  include/linux/gpio/regmap.h |  3 +++
> >  2 files changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpio/gpio-regmap.c b/drivers/gpio/gpio-regmap.c
> > index 87c4225784cf..dac2acb26655 100644
> > --- a/drivers/gpio/gpio-regmap.c
> > +++ b/drivers/gpio/gpio-regmap.c
> > @@ -32,6 +32,8 @@ struct gpio_regmap {
> >  	unsigned int reg_dir_in_base;
> >  	unsigned int reg_dir_out_base;
> >  
> > +	int (*get_direction)(struct gpio_regmap *gpio, unsigned int offset);
> > +
> >  	int (*reg_mask_xlate)(struct gpio_regmap *gpio, unsigned int base,
> >  			      unsigned int offset, unsigned int *reg,
> >  			      unsigned int *mask);
> > @@ -129,6 +131,9 @@ static int gpio_regmap_get_direction(struct gpio_chip *chip,
> >  	unsigned int base, val, reg, mask;
> >  	int invert, ret;
> >  
> > +	if (gpio->get_direction)
> > +		return gpio->get_direction(gpio, offset);
> > +
> >  	if (gpio->reg_dat_base && !gpio->reg_set_base)
> >  		return GPIO_LINE_DIRECTION_IN;
> >  	if (gpio->reg_set_base && !gpio->reg_dat_base)
> > @@ -163,7 +168,16 @@ static int gpio_regmap_set_direction(struct gpio_chip *chip,
> >  {
> >  	struct gpio_regmap *gpio = gpiochip_get_data(chip);
> >  	unsigned int base, val, reg, mask;
> > -	int invert, ret;
> > +	int invert, ret, dir;
> > +
> > +	if (gpio->get_direction) {
> > +		dir = gpio->get_direction(gpio, offset);
> > +		if (dir == GPIO_LINE_DIRECTION_IN && output)
> > +			return -EOPNOTSUPP;
> > +		if (dir == GPIO_LINE_DIRECTION_OUT && !output)
> > +			return -EOPNOTSUPP;
> > +		return 0;
> > +	}
> 
> What is the intention here? Shouldn't there be just a .set_direction
> op and if there isn't one, return EOPNOTSUPP?
> 
> In any case, that is unused code for your driver as far as I see,
> because you neither set .reg_dir_in_base nor .reg_dir_out_base and
> thus, .direction_input nor .direction_output are set within the
> gpio_chip struct (see gpio_regmap_register()).
> 

Yes, you are right. I did want to return ealier an EOPNOTSUPP to make
sure that in my specific case no directions would be changed. But that
is not needed indeed since, as you said, I do not use .reg_dir_in_base
nor .reg_dir_out_base.

I will remove this in v2.

And since we are on the subject, I will try out Andrew's suggestion with
giving gpio-regmap a bitmap to use directly.

Thanks!
Ioana