linux-kernel - Re: [RFC PATCH v2] pinctrl: add helper to expose pinctrl state in debugfs

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Message-ID: <CACRpkdb9RnGJbct+D-88JPDSbaVp1XS8vjhhHYosy20EPkLjaw@mail.gmail.com>
Date:   Sat, 9 Jan 2021 02:22:07 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Drew Fustini <drew@...gleboard.org>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Pantelis Antoniou <pantelis.antoniou@...aro.org>,
        Pantelis Antoniou <pantelis.antoniou@...il.com>,
        Jason Kridner <jkridner@...gleboard.org>,
        Robert Nelson <robertcnelson@...gleboard.org>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [RFC PATCH v2] pinctrl: add helper to expose pinctrl state in debugfs

Hi Drew,

sorry for belated review. The approach is so uncommon so it had me
confused.

On Thu, Dec 24, 2020 at 9:36 PM Drew Fustini <drew@...gleboard.org> wrote:

> > > I used the compatible string "pinctrl,state-helper" but would appreciate
> > > advice on how to best name this. Should I create a new vendor prefix?
> >
> > Here is the first concern. Why does this require to be a driver with a
> > compatible string?
>
> I have not been able to figure out how to have different active pinctrl
> states for each header pins (for example P2 header pin 3) unless they
> are represented as DT nodes with their own compatible for this helper
> driver such as:
>
> &ocp {
>         P2_03_pinmux {
>                 compatible = "pinctrl,state-helper";
>                 pinctrl-names = "default", "gpio", "gpio_pu", "gpio_pd", "gpio_input", "pwm";
>                 pinctrl-0 = <&P2_03_default_pin>;
>                 pinctrl-1 = <&P2_03_gpio_pin>;
>                 pinctrl-2 = <&P2_03_gpio_pu_pin>;
>                 pinctrl-3 = <&P2_03_gpio_pd_pin>;
>                 pinctrl-4 = <&P2_03_gpio_input_pin>;
>                 pinctrl-5 = <&P2_03_pwm_pin>;
>         };
> }

I do not think the DT people are going to appreciate this pseudo-device.

Can you not just represent them as pin control hogs and have the debugfs
code with the other debugfs code in drivers/pinctrl/core.c?

Normal drivers cannot play around with the state assigned to a
hog, but debugfs can certainly do that so go ahead and patch
the core.

> I can assign pinctrl states in the pin controller DT node which has
> compatible pinctrl-single (line 301 arch/arm/boot/dts/am33xx-l4.dtsi):
>
> &am33xx_pinmux {
>
>         pinctrl-names = "default", "gpio", "pwm";
>         pinctrl-0 =   < &P2_03_default_pin &P1_34_default_pin &P2_19_default_pin &P2_24_default_pin
>                         &P2_33_default_pin &P2_22_default_pin &P2_18_default_pin &P2_10_default_pin
>                         &P2_06_default_pin &P2_04_default_pin &P2_02_default_pin &P2_08_default_pin
>                         &P2_17_default_pin >;
>         pinctrl-1 =   < &P2_03_gpio_pin &P1_34_gpio_pin &P2_19_gpio_pin &P2_24_gpio_pin
>                         &P2_33_gpio_pin &P2_22_gpio_pin &P2_18_gpio_pin &P2_10_gpio_pin
>                         &P2_06_gpio_pin &P2_04_gpio_pin &P2_02_gpio_pin &P2_08_gpio_pin
>                         &P2_17_gpio_pin >;
>         pinctrl-2 =   < &P2_03_pwm &P1_34_pwm &P2_19_pwm &P2_24_pwm
>                         &P2_33_pwm &P2_22_pwm &P2_18_pwm &P2_10_pwm
>                         &P2_06_pwm &P2_04_pwm &P2_02_pwm &P2_08_pwm
>                         &P2_17_pwm >;
>
> }
>
> However, there is no way to later select "gpio" for P2.03 and select
> "pwm" for P1.34 at the same time.  Thus, I can not figure out a way to
> select independent states per pin unless I make a node for each pin that
> binds to a helper driver.
>
> It feels like there may be a simpler soluation but I can't see to figure
> it out.  Suggestions welcome!

I think maybe there is no solution because you are solving a problem
that only pinctrl-single while trying to stay generic? The single
driver is special in that it requires all states of pins to be encoded
into the device tree, but for debugging that is kind of unfriendly
which was mentioned in its inception. For deep debugging it is good
to let the core know of all available functions and groups and
single does not IIUC.

Yours,
Linus Walleij