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

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Message-ID: <ab037c11-b0d3-96fc-46cc-858cce6eb35c@redhat.com>
Date:   Mon, 9 Jan 2023 13:02:57 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Wolfram Sang <wsa@...nel.org>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        jarkko.nikula@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
        mika.westerberg@...ux.intel.com, jsd@...ihalf.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

Hi,

On 1/9/23 13:01, Wolfram Sang wrote:
> 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.

This fixes a system suspend/resume bug, so this really should go
to for-current.

Regards,

Hans