linux-kernel - Re: [PATCH v4] i2c: designware: Fix unbalanced suspended flag

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Message-ID: <Y7wCLAJxuR38qJNI@ninjato>
Date:   Mon, 9 Jan 2023 13:01:48 +0100
From:   Wolfram Sang <wsa@...nel.org>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>
Cc:     jarkko.nikula@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
        mika.westerberg@...ux.intel.com, jsd@...ihalf.com,
        hdegoede@...hat.com, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, patches@...nsource.cirrus.com
Subject: Re: [PATCH v4] i2c: designware: Fix unbalanced suspended flag

On Mon, Dec 19, 2022 at 01:01:45PM +0000, Richard Fitzgerald wrote:
> Ensure that i2c_mark_adapter_suspended() is always balanced by a call to
> i2c_mark_adapter_resumed().
> 
> dw_i2c_plat_resume() must always be called, so that
> i2c_mark_adapter_resumed() is called. This is not compatible with
> DPM_FLAG_MAY_SKIP_RESUME, so remove the flag.
> 
> Since the controller is always resumed on system resume the
> dw_i2c_plat_complete() callback is redundant and has been removed.
> 
> The unbalanced suspended flag was introduced by commit c57813b8b288
> ("i2c: designware: Lock the adapter while setting the suspended flag")
> 
> Before that commit, the system and runtime PM used the same functions. The
> DPM_FLAG_MAY_SKIP_RESUME was used to skip the system resume if the driver
> had been in runtime-suspend. If system resume was skipped, the suspended
> flag would be cleared by the next runtime resume. The check of the
> suspended flag was _after_ the call to pm_runtime_get_sync() in
> i2c_dw_xfer(). So either a system resume or a runtime resume would clear
> the flag before it was checked.
> 
> Having introduced the unbalanced suspended flag with that commit, a further
> commit 80704a84a9f8
> ("i2c: designware: Use the i2c_mark_adapter_suspended/resumed() helpers")
> 
> changed from using a local suspended flag to using the
> i2c_mark_adapter_suspended/resumed() functions. These use a flag that is
> checked by I2C core code before issuing the transfer to the bus driver, so
> there was no opportunity for the bus driver to runtime resume itself before
> the flag check.
> 
> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> Fixes: c57813b8b288 ("i2c: designware: Lock the adapter while setting the suspended flag")
> Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Does this fix a bug when runtime resuming? This is not clear to me. I
tend to put it to for-next rather than for-current.


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