linux-kernel - Re: [PATCH V5 2/3] pinctrl: Add support pin control for UP board CPLD/FPGA

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Message-ID: <CACRpkdZZ020mQ8MuKzjab3_qwEcPuQ8=OcrRAz6OtN+B9_JgUw@mail.gmail.com>
Date:   Thu, 10 Aug 2023 13:41:29 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     "larry.lai" <larry.lai@...jingtech.com>
Cc:     lee@...nel.org, andriy.shevchenko@...ux.intel.com, pavel@....cz,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-leds@...r.kernel.org, GaryWang@...on.com.tw,
        musa.lin@...jingtech.com, michael.wang@...jingtech.com,
        jack.chang@...jingtech.com, noah.hung@...jingtech.com
Subject: Re: [PATCH V5 2/3] pinctrl: Add support pin control for UP board CPLD/FPGA

Hi Larry,

thanks for your patch!

I would really like Andy to look at this, because ACPI and I'm not good at
ACPI.

On Tue, Aug 8, 2023 at 4:57 PM larry.lai <larry.lai@...jingtech.com> wrote:

> The UP Squared board <http://www.upboard.com> implements certain
> features (pin control) through an on-board FPGA.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Gary Wang <garywang@...on.com.tw>
> Signed-off-by: larry.lai <larry.lai@...jingtech.com>
(...)

> +               if (strstr(pctrl->pctldesc->pins[offset[i]].name, "I2C") ||
> +                   strstr(pctrl->pctldesc->pins[offset[i]].name, "PINMUX")) {

I think there is something like match a string list in the kernel,
Andy will know.

> +static int upboard_gpio_get(struct gpio_chip *gc, unsigned int offset)
> +{
> +       struct upboard_pinctrl *pctrl = container_of(gc, struct upboard_pinctrl, chip);
> +       unsigned int pin = pctrl->rpi_mapping[offset];
> +       int gpio = upboard_rpi_to_native_gpio(gc, offset);
> +
> +       if (gpio < 0)
> +               return gpio;
> +
> +       /* APL03 board open drain GPIO */
> +       if (pctrl->ident == BOARD_UP_APL03) {
> +               int val = 0;
> +
> +               switch (pin) {
> +               case 0:
> +               case 1:
> +               case 9:
> +               case 23:
> +                       val = readl(pctrl->pins[pin].regs);
> +                       return val & 0x00000003;
> +               default:
> +                       break;
> +               }
> +       }
> +
> +       return gpiod_get_value(gpio_to_desc(gpio));

I don't really like this construction bouncing us back into the global GPIO
numberspace to get to the descriptor of the corresponding native GPIO.
gpio_to_desc() is an uglyhack and shall not be used.

You need to come up with something better here: request all the underlying
GPIO descriptors with gpiod_get(dev, .. ASIS) and store them in an array.
Look in e.g.
drivers/gpio/gpio-aggregator.c
drivers/gpio/gpio-latch.c
for examples of how we do this in other drivers.

The underlying GPIO lines need to be specified somehow, in worst case
using descriptor tables.

> +/* DMI Matches for older bios without fpga initialization */
> +static const struct dmi_system_id upboard_dmi_table[] __initconst = {
> +       {
> +               .ident = BOARD_U

A DMI table OK....

> +static struct platform_driver upboard_pinctrl_driver = {
> +       .driver = {
> +               .name = "upboard-pinctrl",
> +       },
> +};
> +module_platform_driver_probe(upboard_pinctrl_driver, upboard_pinctrl_probe);

OK I don't know ACPI, but what I've seen the DMI table is supposed
to be used for some kind of lookup, such as checking in .init if the
device is there, so I don't get this. Also doesn't ACPI drivers use
the ACPI bus?

Yours,
Linus Walleij