linux-kernel - Re: [PATCH v5 2/5] gpiolib: Add support for GPIO line table lookup

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Date:   Wed, 19 Feb 2020 11:17:00 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Harish Jenny K N <harish_kandiga@...tor.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Alexander Graf <graf@...zon.com>,
        Peter Maydell <peter.maydell@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Phil Reid <preid@...ctromag.com.au>,
        Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        QEMU Developers <qemu-devel@...gnu.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v5 2/5] gpiolib: Add support for GPIO line table lookup

On Tue, Feb 18, 2020 at 4:18 PM Geert Uytterhoeven
<geert+renesas@...der.be> wrote:
> Currently GPIOs can only be referred to by GPIO controller and offset in
> GPIO lookup tables.
>
> Add support for looking them up by line name.
> Rename gpiod_lookup.chip_label to gpiod_lookup.key, to make it clear
> that this field can have two meanings, and update the kerneldoc and
> GPIO_LOOKUP*() macros.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Reviewed-by: Ulrich Hecht <uli+renesas@...nd.eu>
> Reviewed-by: Eugeniu Rosca <erosca@...adit-jv.com>
> Tested-by: Eugeniu Rosca <erosca@...adit-jv.com>

> --- a/include/linux/gpio/machine.h
> +++ b/include/linux/gpio/machine.h
> @@ -20,8 +20,9 @@ enum gpio_lookup_flags {
>
>  /**
>   * struct gpiod_lookup - lookup table
> - * @chip_label: name of the chip the GPIO belongs to
> - * @chip_hwnum: hardware number (i.e. relative to the chip) of the GPIO
> + * @key: either the name of the chip the GPIO belongs to, or the GPIO line name
> + * @chip_hwnum: hardware number (i.e. relative to the chip) of the GPIO, or
> + *              U16_MAX to indicate that @key is a GPIO line name
>   * @con_id: name of the GPIO from the device's point of view
>   * @idx: index of the GPIO in case several GPIOs share the same name
>   * @flags: bitmask of gpio_lookup_flags GPIO_* values
> @@ -30,7 +31,7 @@ enum gpio_lookup_flags {
>   * functions using platform data.
>   */
>  struct gpiod_lookup {
> -       const char *chip_label;
> +       const char *key;
>         u16 chip_hwnum;
>         const char *con_id;
>         unsigned int idx;

This needs an update in the documentation:

--- a/Documentation/driver-api/gpio/board.rst
+++ b/Documentation/driver-api/gpio/board.rst
@@ -113,13 +113,15 @@ files that desire to do so need to include the
following header::
 GPIOs are mapped by the means of tables of lookups, containing instances of the
 gpiod_lookup structure. Two macros are defined to help declaring such
mappings::

-       GPIO_LOOKUP(chip_label, chip_hwnum, con_id, flags)
-       GPIO_LOOKUP_IDX(chip_label, chip_hwnum, con_id, idx, flags)
+       GPIO_LOOKUP(key, chip_hwnum, con_id, flags)
+       GPIO_LOOKUP_IDX(key, chip_hwnum, con_id, idx, flags)

 where

-  - chip_label is the label of the gpiod_chip instance providing the GPIO
-  - chip_hwnum is the hardware number of the GPIO within the chip
+  - key is either the label of the gpiod_chip instance providing the GPIO, or
+    the GPIO line name
+  - chip_hwnum is the hardware number of the GPIO within the chip, or U16_MAX
+    to indicate that key is a GPIO line name
   - con_id is the name of the GPIO function from the device point of view. It
        can be NULL, in which case it will match any function.
   - idx is the index of the GPIO within the function.


Furthermore, a few drivers populate the gpiod_lookup members directly,
instead of using the convenience macros:

    arch/arm/mach-integrator/impd1.c
    drivers/i2c/busses/i2c-i801.c
    drivers/mfd/sm501.c

Either they have to be updated s/chip_label/key/, or start using the macros,
e.g.

--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -1444,9 +1444,9 @@ static int i801_add_mux(struct i801_priv *priv)
                return -ENOMEM;
        lookup->dev_id = "i2c-mux-gpio";
        for (i = 0; i < mux_config->n_gpios; i++) {
-               lookup->table[i].chip_label = mux_config->gpio_chip;
-               lookup->table[i].chip_hwnum = mux_config->gpios[i];
-               lookup->table[i].con_id = "mux";
+               lookup->table[i] = (struct gpiod_lookup)
+                       GPIO_LOOKUP(mux_config->gpio_chip,
+                                   mux_config->gpios[i], "mux", 0);
        }
        gpiod_add_lookup_table(lookup);
        priv->lookup = lookup;

Do you have any preference?
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds