linux-kernel - Re: [PATCH v3 05/10] gpio: regmap: add the .fixed_direction

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Message-ID: <CAMRc=MdxE-qsthHot7+iA8yqg1ZEASzGh7dmR=ucfxg_JQipxQ@mail.gmail.com>
Date: Thu, 18 Sep 2025 03:55:16 -0700
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Ioana Ciornei <ioana.ciornei@....com>
Cc: Frank Li <Frank.Li@....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>, Michael Walle <mwalle@...nel.org>, Lee Jones <lee@...nel.org>, 
	devicetree@...r.kernel.org, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 05/10] gpio: regmap: add the .fixed_direction_output
 configuration parameter

On Wed, 17 Sep 2025 11:04:17 +0200, Ioana Ciornei <ioana.ciornei@....com> said:
> 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.
>
> Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
> ---
> Changes in v2:
> - Add the fixed_direction_output bitmap to the gpio_regmap_config
> Changes in v3:
> - Make a deep copy of the new bitmap.
> - Remove the offset check against the ngpio.
> - Added documentation for the new config field.
>
>  drivers/gpio/gpio-regmap.c  | 18 ++++++++++++++++++
>  include/linux/gpio/regmap.h |  6 ++++++
>  2 files changed, 24 insertions(+)
>
> diff --git a/drivers/gpio/gpio-regmap.c b/drivers/gpio/gpio-regmap.c
> index e8a32dfebdcb..9edd79b5c10e 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 +130,13 @@ static int gpio_regmap_get_direction(struct gpio_chip *chip,
>  	unsigned int base, val, reg, mask;
>  	int invert, ret;
>
> +	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)
> @@ -277,6 +285,16 @@ struct gpio_regmap *gpio_regmap_register(const struct gpio_regmap_config *config
>  			return ERR_PTR(ret);
>  	}
>
> +	if (config->fixed_direction_output) {
> +		gpio->fixed_direction_output = devm_bitmap_alloc(config->parent,
> +								 chip->ngpio,
> +								 GFP_KERNEL);

Please don't use devres hidden in what is effectively a library function for
drivers. You have no guarantee this will always be used in probe or that the
life-time of this will end with the associated device's detach. Just use
a regular bitmap_alloc().

Bart

> +		if (!gpio->fixed_direction_output)
> +			return ERR_PTR(-ENOMEM);
> +		bitmap_copy(gpio->fixed_direction_output,
> +			    config->fixed_direction_output, chip->ngpio);
> +	}
> +
>  	/* if not set, assume there is only one register */
>  	gpio->ngpio_per_reg = config->ngpio_per_reg;
>  	if (!gpio->ngpio_per_reg)
> diff --git a/include/linux/gpio/regmap.h b/include/linux/gpio/regmap.h
> index c722c67668c6..8d3d595bfdd3 100644
> --- a/include/linux/gpio/regmap.h
> +++ b/include/linux/gpio/regmap.h
> @@ -37,6 +37,10 @@ struct regmap;
>   *			offset to a register/bitmask pair. If not
>   *			given the default gpio_regmap_simple_xlate()
>   *			is used.
> + * @fixed_direction_output:
> + *			(Optional) Bitmap representing the fixed direction of
> + *			the GPIO lines. Useful when there are GPIO lines with a
> + *			fixed direction mixed together in the same register.
>   * @drvdata:		(Optional) Pointer to driver specific data which is
>   *			not used by gpio-remap but is provided "as is" to the
>   *			driver callback(s).
> @@ -78,6 +82,8 @@ struct gpio_regmap_config {
>  	int ngpio_per_reg;
>  	struct irq_domain *irq_domain;
>
> +	unsigned long *fixed_direction_output;
> +
>  	int (*reg_mask_xlate)(struct gpio_regmap *gpio, unsigned int base,
>  			      unsigned int offset, unsigned int *reg,
>  			      unsigned int *mask);
> --
> 2.25.1
>
>