Re: [RFC v2 5/5] dt-bindings: gpio: Add bindings for pinctrl based generic gpio driver

From: AKASHI Takahiro <takahiro.akashi@linaro.org>
To: Cristian Marussi <cristian.marussi@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	Rob Herring <robh@kernel.org>,
	sudeep.holla@arm.com, krzysztof.kozlowski+dt@linaro.org,
	conor+dt@kernel.org, Oleksii_Moisieiev@epam.com,
	linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org
Subject: Re: [RFC v2 5/5] dt-bindings: gpio: Add bindings for pinctrl based generic gpio driver
Date: Tue, 10 Oct 2023 14:14:37 +0900	[thread overview]
Message-ID: <ZSTdvROVzJU5FRAZ@octopus> (raw)
In-Reply-To: <ZSQXXW1NRiCpsENu@e120937-lin>

On Mon, Oct 09, 2023 at 04:08:13PM +0100, Cristian Marussi wrote:
> On Mon, Oct 09, 2023 at 03:13:24PM +0200, Linus Walleij wrote:
> > On Mon, Oct 9, 2023 at 11:08???AM Cristian Marussi
> > <cristian.marussi@arm.com> wrote:
> > 
> > > > > +    gpio0: gpio@0 {
> > > > > +        compatible = "pin-control-gpio";
> > > > > +        gpio-controller;
> > > > > +        #gpio-cells = <2>;
> > > > > +        gpio-ranges = <&scmi_pinctrl 0 10 5>,
> > > > > +                      <&scmi_pinctrl 5 0 0>;
> > > > > +        gpio-ranges-group-names = "",
> > > > > +                                  "pinmux_gpio";
> > > > > +    };
> > > >
> > >
> > > Assuming the above &scmi_pinctrl refers to the protocol node as we
> > > usually do,
> > 
> > No it does not, it is a three-layer cake.
> > 
> > scmi <-> scmi_pinctrl <-> scmi_gpio
> > 
> > it refers to the scmi_pinctrl node.
> > 
> 
> Thanks, this explains a lot.
> Cristian

Just in case, 

    gpio-ranges = <&scmi_pinctrl 0 10 5>;

means that SCMI *pin* range [10..(10+5-1)] are mapped to this driver's
gpio range [0..(5-1)]. So any consumer driver can access a gpio pin
as:
    foo-gpios = <&gpio0 3>;

will refer to gpio pin#3 that is actually SCMI's 13.

    gpio-ranges = <&scmi_pinctrl 5 0 0>;
    gpio-ranges-group-names = "pinmux_gpio";

means that SCMI *group*, "pinmux_gpio", are mapped to this driver's
gpio range which starts with 5. If "pinmux_gpio" indicates SCMI *pin*
range [20..24],

    baa-gpios = <&gpio0 7>;
will refer to gpio pin#7 that is actually SCMI's 22 (=20 + (7-5)).

This way, we (consumer drivers) don't care what is the underlying pin
controller.

-Takahiro Akashi

> 
> > There is no SCMI GPIO protocol, instead SCMI is using the
> > operations already available in the pin controller to exercise
> > GPIO. Generic pin control has operations to drive lines for
> > example, and Takahiro is adding the ability for a generic pin
> > controller to also read a line.
> 
> 
> > 
> > Yours,
> > Linus Walleij