linux-kernel - Re: [PATCH v4 1/6] i2c: Allow driver to manage the device's power state during probe

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Date:   Wed, 29 Jan 2020 14:54:20 +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 1/6] i2c: Allow driver to manage the device's power
 state during probe

wt., 21 sty 2020 o 14:41 Sakari Ailus <sakari.ailus@...ux.intel.com> napisał(a):
>
> Enable drivers to tell ACPI that there's no need to power on a device for
> probe. Drivers should still perform this by themselves if there's a need
> to. In some cases powering on the device during probe is undesirable, and
> this change enables a driver to choose what fits best for it.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/i2c/i2c-core-base.c | 15 ++++++++++++---
>  include/linux/i2c.h         |  3 +++
>  2 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 9f8dcd3f83850..7bf1699c9044d 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -303,6 +303,14 @@ static int i2c_smbus_host_notify_to_irq(const struct i2c_client *client)
>         return irq > 0 ? irq : -ENXIO;
>  }
>
> +static bool probe_low_power(struct device *dev)
> +{
> +       struct i2c_driver *driver = to_i2c_driver(dev->driver);
> +
> +       return driver->probe_low_power &&
> +               device_property_present(dev, "probe-low-power");
> +}
> +
>  static int i2c_device_probe(struct device *dev)
>  {
>         struct i2c_client       *client = i2c_verify_client(dev);
> @@ -375,7 +383,8 @@ static int i2c_device_probe(struct device *dev)
>         if (status < 0)
>                 goto err_clear_wakeup_irq;
>
> -       status = dev_pm_domain_attach(&client->dev, true);
> +       status = dev_pm_domain_attach(&client->dev,
> +                                     !probe_low_power(&client->dev));
>         if (status)
>                 goto err_clear_wakeup_irq;
>
> @@ -397,7 +406,7 @@ static int i2c_device_probe(struct device *dev)
>         return 0;
>
>  err_detach_pm_domain:
> -       dev_pm_domain_detach(&client->dev, true);
> +       dev_pm_domain_detach(&client->dev, !probe_low_power(&client->dev));
>  err_clear_wakeup_irq:
>         dev_pm_clear_wake_irq(&client->dev);
>         device_init_wakeup(&client->dev, false);
> @@ -419,7 +428,7 @@ static int i2c_device_remove(struct device *dev)
>                 status = driver->remove(client);
>         }
>
> -       dev_pm_domain_detach(&client->dev, true);
> +       dev_pm_domain_detach(&client->dev, !probe_low_power(&client->dev));
>
>         dev_pm_clear_wake_irq(&client->dev);
>         device_init_wakeup(&client->dev, false);
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 582ef05ec07ed..6d0d6af393c56 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -229,6 +229,8 @@ enum i2c_alert_protocol {
>   * @address_list: The I2C addresses to probe (for detect)
>   * @clients: List of detected clients we created (for i2c-core use only)
>   * @disable_i2c_core_irq_mapping: Tell the i2c-core to not do irq-mapping
> + * @probe_low_power: Let the driver manage the device's power state
> + *                  during probe and remove.
>   *
>   * The driver.owner field should be set to the module owner of this driver.
>   * The driver.name field should be set to the name of this driver.
> @@ -289,6 +291,7 @@ struct i2c_driver {
>         struct list_head clients;
>
>         bool disable_i2c_core_irq_mapping;
> +       bool probe_low_power;

I don't see any users of disable_i2c_core_irq_mapping in current
mainline. Maybe instead of adding another 1-byte boolean for every
such property, let's just use the fact that this struct will have at
least an alignment of 32-bits anyway and merge the two into an int
field called 'flags' so that we can extend it in the future if needed?

The name 'probe_low_power' is misleading to me too. It makes me think
it's the default state for some reason. It should be something like
'allow_low_power_probe'.

Bartosz

>  };
>  #define to_i2c_driver(d) container_of(d, struct i2c_driver, driver)
>
> --
> 2.20.1
>