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

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Message-ID: <tsgdrm6qetvepolbyxjral3ark7yrtwi5zyazras3ka2xjax77@hds2kvc3nzda>
Date: Thu, 10 Jul 2025 12:23:39 +0300
From: Ioana Ciornei <ioana.ciornei@....com>
To: Andrew Lunn <andrew@...n.ch>
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>, 
	Michael Walle <mwalle@...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 05:09:17PM +0200, Andrew Lunn wrote:
> On Wed, Jul 09, 2025 at 02:26:53PM +0300, 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.
> > 
> > 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);
> > +
> 
> This is not my area, so i will deffer to the GPIO
> Maintainers. However, it is not clear to me what get_direction()
> should return. Is it the current direction, or the supported
> directions? Maybe it should be called get_fixed_direction()?
> 
> I then wounder how it will be implemented. Since it is fixed, it is
> probably just a constant bitmap, and you look at the offset bit in
> this batmap? At minimum a ready made helper could be provided, or
> rather than have this op, just provide the bitmap, and gpio-regmap.c
> can look at the bit in the bitmap?
>

That is indeed possible and would save us from an extra callback that
doesn't do much, it just looks into the same kind of bitmap that
gpio-regmap could just have access to directly.

I will wait for feedback from the GPIO maintainers but I do like the
idea.

Thanks!