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

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Message-ID: <4awrlgj33bg33gg4ianqk5ypchrygppkqyyojfliznitbtzu5h@xsgnk25syvqq>
Date: Mon, 15 Sep 2025 16:55:37 +0300
From: Ioana Ciornei <ioana.ciornei@....com>
To: Michael Walle <mwalle@...nel.org>
Cc: 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, Frank Li <Frank.Li@....com>
Subject: Re: [PATCH v2 4/9] gpio: regmap: add the .fixed_direction_output
 configuration parameter

On Mon, Sep 15, 2025 at 02:45:58PM +0200, Michael Walle wrote:
> 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)

Yes, I missed that memory leak. Sorry.

> 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.

So you are suggesting gpio-regmap to allocate the bitmap using
devm_bitmap_alloc() and base its size on config->ngpio, then copy into
it the bitmap passed by the caller, right?  Yes, that does seem more
error proof in terms of memory handling. Will change it in the next
version.

> 
> 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.

Ok, sure.

Ioana