linux-kernel - Re: [PATCH 01/10] i2c: add suspended flag and accessors for i2c adapters

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Date:   Wed, 19 Dec 2018 18:22:50 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     linux-i2c@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Wolfram Sang <wsa@...-dreams.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/10] i2c: add suspended flag and accessors for i2c
 adapters

On Wed, Dec 19, 2018 at 05:48:17PM +0100, Wolfram Sang wrote:
> +static inline void i2c_mark_adapter_suspended(struct i2c_adapter *adap)
> +{
> +	i2c_lock_bus(adap, I2C_LOCK_ROOT_ADAPTER);
> +	set_bit(I2C_ALF_IS_SUSPENDED, &adap->locked_flags);
> +	i2c_unlock_bus(adap, I2C_LOCK_ROOT_ADAPTER);
> +}

This looks like a duplication of the is_suspended flag in struct dev_pm_info.
Any reason why you can't use that?  If so, it would be good to document the
reason in the commit message.

If the point is to constrain refusal of transfers in suspended state to
certain drivers, those drivers could opt in to that functionality by
setting a flag, and the i2c core could then gate refusal based on
that flag and the is_suspended flag in struct dev_pm_info.

Also, why is it necessary to take a lock to perform an atomic bitop?
(Sorry if that's a dumb question, seems non-obvious to me.)

Thanks,

Lukas