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SubjectRe: [PATCH v4] PM / devfreq: Restart previous governor if new governor fails to start
On 2019-03-05 12:48, MyungJoo Ham wrote:
>> Hey MyungJoo, Kyungmin
>> Did you get a chance to think about how you
>> want this fix implemented?
>>
>> On 2019-02-19 10:42, Sibi Sankar wrote:
>>> Hey MyungJoo,
>>>
>>> On 12/14/18 7:15 AM, MyungJoo Ham wrote:
>>>>> From: Saravana Kannan <skannan@codeaurora.org>
>>>>>
>>>>> If the new governor fails to start, switch back to old governor so
>>>>> that the
>>>>> devfreq state is not left in some weird limbo.
>>>>>
>>>>> Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
>>>>> Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
>>>>> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
>>>>
>>>> Hello,
>>>>
>>>> In overall, the idea and the implementation looks good.
>>>>
>>>> However, I have a question:
>>>>
>>>> What if the following line fails?
>>>>
>>>> + df->governor->event_handler(df, DEVFREQ_GOV_START,
>>>> + NULL);
>>>>
>>>> Don't we still need something to handle for such events?
>>>
>>> The original discussion went as follows:
>>> governor_store is expected to be used only on cases
>>> where devfreq_add_device() succeeded i.e prev->governor
>>> is expected to be present and DEVFREQ_GOV_START is
>>> expected to succeed. Hence falling back to the previous
>>> governor seems like a sensible idea.
>>>
>>> This would also prevent DEVFREQ_GOV_STOP from being called
>>> on a governor were DEVFREQ_GOV_START had failed which is
>>> ideal.
>>>
>>> That being said DEVFREQ_GOV_START can still fail for the
>>> prev-governor due to some change in state of the system.
>>> Do you want to handle this case by clearing the state of
>>> governor rather than switching to previous governor?
>>>
>
> If moving back to previous governor fails after
> failing for "next" governor, we may assume it's fatal
> and stop the device; we can simply return errors.
>
> In such a case, df->governor may need to be NULL as well.

Thanks. Will make the necessary changes in the
next re-spin.

>
>
> Cheers,
> MyungJoo

--
-- Sibi Sankar --
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project.

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