linux-kernel - Re: [PATCH v2 1/2] gpio: tps65219: add GPIO support for TPS65219 PMIC

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Message-ID: <CACRpkdbjjoOoGeaqv9yQ4fTKqxt5eLDBjZCnNAYQnng3L+n8TQ@mail.gmail.com>
Date:   Thu, 11 May 2023 22:57:46 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Jerome Neanne <jneanne@...libre.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Tony Lindgren <tony@...mide.com>, Lee Jones <lee@...nel.org>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-omap@...r.kernel.org,
        Jonathan Cormier <jcormier@...ticallink.com>
Subject: Re: [PATCH v2 1/2] gpio: tps65219: add GPIO support for TPS65219 PMIC

On Thu, May 11, 2023 at 4:09 PM Jerome Neanne <jneanne@...libre.com> wrote:

> Add support for TPS65219 PMICs GPIO interface.
>
> 3 GPIO pins:
> - GPIO0 only is IO but input mode reserved for MULTI_DEVICE_ENABLE usage
> - GPIO1 and GPIO2 are Output only and referred as GPO1 and GPO2 in spec
>
> GPIO0 is statically configured as input or output prior to Linux boot.
> it is used for MULTI_DEVICE_ENABLE function.
> This setting is statically configured by NVM.
> GPIO0 can't be used as a generic GPIO (specification Table 8-34).
> It's either a GPO when MULTI_DEVICE_EN=0,
> or a GPI when MULTI_DEVICE_EN=1.
>
> Datasheet describes specific usage for non standard GPIO.
> Link: https://www.ti.com/lit/ds/symlink/tps65219.pdf
>
> Co-developed-by: Jonathan Cormier <jcormier@...ticallink.com>
> Signed-off-by: Jonathan Cormier <jcormier@...ticallink.com>
> Signed-off-by: Jerome Neanne <jneanne@...libre.com>
(...)

This overall looks fine.

> +static int tps65219_gpio_change_direction(struct gpio_chip *gc, unsigned int offset,
> +                                         unsigned int direction)
> +{
> +       struct tps65219_gpio *gpio = gpiochip_get_data(gc);
> +
> +       /* Documentation is stating that GPIO0 direction must not be changed in Linux:
> +        * Table 8-34. MFP_1_CONFIG(3): MULTI_DEVICE_ENABLE,
> +        * Should only be changed in INITIALIZE state (prior to ON Request).
> +        * Set statically by NVM, changing direction in application can cause a hang.
> +        * Below can be used for test purpose only:
> +        */
> +
> +#if 0
> +       int ret = regmap_update_bits(gpio->tps->regmap, TPS65219_REG_MFP_1_CONFIG,
> +                                TPS65219_GPIO0_DIR_MASK, direction);
> +       if (ret)
> +               return ret;
> +#endif
> +       dev_err(gpio->tps->dev,
> +               "GPIO%d direction set by NVM, change to %u failed, not allowed by specification\n",
> +                offset, direction);
> +       return -EOPNOTSUPP;
> +}

Normally people would complain about #if 0 code.

But this is a special case!

I definitely want the code to be in there somehow.

What about:

if (IS_ENABLED(DEBUG))?

If someone enables debug with an explicit -DDEBUG to the compiler
this could be allowed.

Yours,
Linus Walleij

Yours,
Linus Walleij