linux-kernel - Re: [PATCH v5 1/6] i2c: Allow driver to manage the device's power state during probe

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Date:   Mon, 10 Aug 2020 15:41:48 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     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@...r.kernel.org,
        Chiranjeevi Rapolu <chiranjeevi.rapolu@...el.com>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rajmohan.mani@...el.com, Tomasz Figa <tfiga@...omium.org>,
        Sudeep Holla <sudeep.holla@....com>,
        "Qiu, Tian Shu" <tian.shu.qiu@...el.com>
Subject: Re: [PATCH v5 1/6] i2c: Allow driver to manage the device's power
 state during probe

On Mon, Aug 10, 2020 at 05:27:42PM +0300, Sakari Ailus wrote:
> 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.
>
> Add a field called "flags" into struct i2c_driver for driver flags, and a
> flag I2C_DRV_FL_ALLOW_LOW_POWER_PROBE to tell a driver supports probe in
> low power state.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/i2c/i2c-core-base.c | 17 ++++++++++++++---
>  include/linux/i2c.h         | 14 ++++++++++++++
>  2 files changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 34a9609f256da..cde9cf49a07e6 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -436,6 +436,14 @@ static int i2c_smbus_host_notify_to_irq(const struct i2c_client *client)
>  	return irq > 0 ? irq : -ENXIO;
>  }
>
> +static bool allow_low_power_probe(struct device *dev)
> +{
> +	struct i2c_driver *driver = to_i2c_driver(dev->driver);
> +
> +	return driver->flags & I2C_DRV_FL_ALLOW_LOW_POWER_PROBE &&
> +		device_property_present(dev, "allow-low-power-probe");

I assume this change makes even the DT property "allow-low-power-probe"
work in the same way. Should we have proper DT binding for that ?

This comment applies for any property using device_property_* but has
no explicit DT binding ? Just asking the question to know the strategy
followed. Sorry if this is redundant question, feel free to point me
to the past discussions.

--
Regards,
Sudeep