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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Thu, 2 Jul 2020 15:36:32 +0300
Message-ID: <CAHp75VdSWxcAQzWryKoMfzh8xM_2ZRF6Uk+8pveGhmt=prOAVg@mail.gmail.com>
Subject: Re: [PATCH v4 1/2] gpio: add GPO driver for PCA9570
To:     Sungbo Eo <mans0n@gorani.run>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Michael Walle <michael@walle.cc>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>
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On Thu, Jul 2, 2020 at 3:18 PM Sungbo Eo <mans0n@gorani.run> wrote:
>
> NXP PCA9570 is 4-bit I2C GPO expander without interrupt functionality.

is a 4-bit

> Its ports are controlled only by a data byte without register address.
>
> As there is no other driver similar enough to be adapted for it, a new
> driver is introduced here.

Can we have a Datasheet: tag with URL attached to it?

...

> +static int pca9570_read(struct pca9570 *gpio, u8 *value)
> +{
> +       s32 ret;
> +
> +       ret = i2c_smbus_read_byte(gpio->client);
> +       if (ret < 0)
> +               return ret;
> +

> +       *value = (u8)ret;

I doubt casting is needed.

> +       return 0;
> +}

...

> +static const struct i2c_device_id pca9570_id_table[] = {
> +       { "pca9570", 4 },
> +       { /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(i2c, pca9570_id_table);
> +
> +static const struct of_device_id pca9570_of_match_table[] = {

> +       { .compatible = "nxp,pca9570" },

This driver data should also have 4.

> +       { /* sentinel */ }
> +};

...

> +       gpio->chip.ngpio = i2c_match_id(pca9570_id_table, client)->driver_data;

Oh, avoid direct access to the table like this. And you may simply use
device_get_match_data().
...

> +       /* Read the current output level */
> +       (void) pca9570_read(gpio, &gpio->out);

(void) casting is not needed. And I'm not sure hiding an error is a
good idea. But the latter is up to you.

-- 
With Best Regards,
Andy Shevchenko