linux-kernel - Re: [PATCH v4 5/6] at24: Support probing while off

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Date:   Wed, 29 Jan 2020 14:36:17 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     linux-i2c <linux-i2c@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-acpi@...r.kernel.org, Bingbu Cao <bingbu.cao@...el.com>,
        linux-media <linux-media@...r.kernel.org>,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@...el.com>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rajmohan.mani@...el.com, Tomasz Figa <tfiga@...omium.org>
Subject: Re: [PATCH v4 5/6] at24: Support probing while off

wt., 21 sty 2020 o 14:41 Sakari Ailus <sakari.ailus@...ux.intel.com> napisał(a):
>
> In certain use cases (where the chip is part of a camera module, and the
> camera module is wired together with a camera privacy LED), powering on
> the device during probe is undesirable. Add support for the at24 to
> execute probe while being powered off. For this to happen, a hint in form
> of a device property is required from the firmware.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/misc/eeprom/at24.c | 31 +++++++++++++++++++++----------
>  1 file changed, 21 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> index 0681d5fdd538a..5fc1162b67618 100644
> --- a/drivers/misc/eeprom/at24.c
> +++ b/drivers/misc/eeprom/at24.c
> @@ -564,6 +564,7 @@ static int at24_probe(struct i2c_client *client)
>         bool i2c_fn_i2c, i2c_fn_block;
>         unsigned int i, num_addresses;
>         struct at24_data *at24;
> +       bool low_power;
>         struct regmap *regmap;
>         bool writable;
>         u8 test_byte;
> @@ -701,19 +702,24 @@ static int at24_probe(struct i2c_client *client)
>
>         i2c_set_clientdata(client, at24);
>
> -       /* enable runtime pm */
> -       pm_runtime_set_active(dev);
> +       low_power = acpi_dev_state_low_power(&client->dev);
> +       if (!low_power)
> +               pm_runtime_set_active(dev);
> +
>         pm_runtime_enable(dev);
>
>         /*
> -        * Perform a one-byte test read to verify that the
> -        * chip is functional.
> +        * Perform a one-byte test read to verify that the chip is functional,
> +        * unless powering on the device is to be avoided during probe (i.e.
> +        * it's powered off right now).
>          */
> -       err = at24_read(at24, 0, &test_byte, 1);
> -       pm_runtime_idle(dev);
> -       if (err) {
> -               pm_runtime_disable(dev);
> -               return -ENODEV;
> +       if (!low_power) {
> +               err = at24_read(at24, 0, &test_byte, 1);
> +               pm_runtime_idle(dev);
> +               if (err) {
> +                       pm_runtime_disable(dev);
> +                       return -ENODEV;
> +               }
>         }
>
>         if (writable)
> @@ -728,8 +734,12 @@ static int at24_probe(struct i2c_client *client)
>
>  static int at24_remove(struct i2c_client *client)
>  {
> +       bool low_power;
> +
>         pm_runtime_disable(&client->dev);
> -       pm_runtime_set_suspended(&client->dev);
> +       low_power = acpi_dev_state_low_power(&client->dev);

This is inconsistent. You define the low_power field in the context
structure (BTW the name low_power is a bit vague here - without
looking at its assignment it would make me think it's about something
battery-related, how about 'off_at_probe'?) and instead of reusing
this field here, you call acpi_dev_state_low_power() again. Either
don't store the context for the life-time of the device if not
necessary or don't call acpi_dev_state_low_power() at remove, although
the commit message doesn't describe whether the latter is done on
purpose.

Bartosz

> +       if (!low_power)
> +               pm_runtime_set_suspended(&client->dev);
>
>         return 0;
>  }
> @@ -743,6 +753,7 @@ static struct i2c_driver at24_driver = {
>         .probe_new = at24_probe,
>         .remove = at24_remove,
>         .id_table = at24_ids,
> +       .probe_low_power = true,
>  };
>
>  static int __init at24_init(void)
> --
> 2.20.1
>