linux-kernel - Re: [PATCH v2 4/9] gpio: regmap: add the .fixed_direction

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Message-Id: <DCTDUJO0PS8B.1LD03WTEMNRVP@kernel.org>
Date: Mon, 15 Sep 2025 14:45:58 +0200
From: "Michael Walle" <mwalle@...nel.org>
To: "Ioana Ciornei" <ioana.ciornei@....com>, "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>, <devicetree@...r.kernel.org>,
 <linux-gpio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Cc: "Frank Li" <Frank.Li@....com>
Subject: Re: [PATCH v2 4/9] gpio: regmap: add the .fixed_direction_output
 configuration parameter

Hi Ioana,

On Mon Sep 15, 2025 at 2:23 PM CEST, Ioana Ciornei wrote:
> There are GPIO controllers such as the one present in the LX2160ARDB
> QIXIS FPGA which have fixed-direction input and output GPIO lines mixed
> together in a single register. This cannot be modeled using the
> gpio-regmap as-is since there is no way to present the true direction of
> a GPIO line.
>
> In order to make this use case possible, add a new configuration
> parameter - fixed_direction_output - into the gpio_regmap_config
> structure. This will enable user drivers to provide a bitmap that
> represents the fixed direction of the GPIO lines.

I wonder about the ownership of that allocated memory in the config
structure (and btw, I guess you leak the memory in your driver) and
if it's not better and more error proof to allocate and copy the
bitmap in gpio-regmap too (and maybe use devm_bitmap_alloc()) and
leave it to the caller to handle the passed bitmap. I.e. it could
also be on the stack.

Otherwise, this looks good.

> Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
> ---
> Changes in v2:
> - Add the fixed_direction_output bitmap to the gpio_regmap_config
>
>  drivers/gpio/gpio-regmap.c  | 12 ++++++++++++
>  include/linux/gpio/regmap.h |  2 ++
>  2 files changed, 14 insertions(+)
>
> diff --git a/drivers/gpio/gpio-regmap.c b/drivers/gpio/gpio-regmap.c
> index e8a32dfebdcb..2489768686d3 100644
> --- a/drivers/gpio/gpio-regmap.c
> +++ b/drivers/gpio/gpio-regmap.c
> @@ -31,6 +31,7 @@ struct gpio_regmap {
>  	unsigned int reg_clr_base;
>  	unsigned int reg_dir_in_base;
>  	unsigned int reg_dir_out_base;
> +	unsigned long *fixed_direction_output;
>  
>  	int (*reg_mask_xlate)(struct gpio_regmap *gpio, unsigned int base,
>  			      unsigned int offset, unsigned int *reg,
> @@ -129,6 +130,16 @@ static int gpio_regmap_get_direction(struct gpio_chip *chip,
>  	unsigned int base, val, reg, mask;
>  	int invert, ret;
>  
> +	if (offset >= chip->ngpio)
> +		return -EINVAL;

Not sure this can happen. I tried to look into gpiolib.c but
couldn't find anything obvious that it can't happen. Maybe Linus or
Bartosz can comment on that.

> +
> +	if (gpio->fixed_direction_output) {
> +		if (test_bit(offset, gpio->fixed_direction_output))
> +			return GPIO_LINE_DIRECTION_OUT;
> +		else
> +			return GPIO_LINE_DIRECTION_IN;
> +	}
> +
>  	if (gpio->reg_dat_base && !gpio->reg_set_base)
>  		return GPIO_LINE_DIRECTION_IN;
>  	if (gpio->reg_set_base && !gpio->reg_dat_base)
> @@ -247,6 +258,7 @@ struct gpio_regmap *gpio_regmap_register(const struct gpio_regmap_config *config
>  	gpio->reg_clr_base = config->reg_clr_base;
>  	gpio->reg_dir_in_base = config->reg_dir_in_base;
>  	gpio->reg_dir_out_base = config->reg_dir_out_base;
> +	gpio->fixed_direction_output = config->fixed_direction_output;
>  
>  	chip = &gpio->gpio_chip;
>  	chip->parent = config->parent;
> diff --git a/include/linux/gpio/regmap.h b/include/linux/gpio/regmap.h
> index c722c67668c6..34c143aca42d 100644
> --- a/include/linux/gpio/regmap.h
> +++ b/include/linux/gpio/regmap.h
> @@ -78,6 +78,8 @@ struct gpio_regmap_config {
>  	int ngpio_per_reg;
>  	struct irq_domain *irq_domain;
>  
> +	unsigned long *fixed_direction_output;

Please add some documentation.

-michael

> +
>  	int (*reg_mask_xlate)(struct gpio_regmap *gpio, unsigned int base,
>  			      unsigned int offset, unsigned int *reg,
>  			      unsigned int *mask);


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