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From: Sibi Sankar <sibis@codeaurora.org>
To: myungjoo.ham@samsung.com, Kyungmin Park <kyungmin.park@samsung.com>
Cc: Chanwoo Choi <cw00.choi@samsung.com>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-arm-msm-owner@vger.kernel.org" 
	<linux-arm-msm-owner@vger.kernel.org>,
	"skannan@codeaurora.org" <skannan@codeaurora.org>
Subject: Re: [PATCH v4] PM / devfreq: Restart previous governor if new governor fails to start
Date: Tue, 19 Feb 2019 10:42:01 +0530
Message-ID: <39d3a906-b734-9bb8-c60a-48948bb21338@codeaurora.org> (raw)
In-Reply-To: <20181214014527epcms1p6c783b4cd1602bbcbcb6e725f840db479@epcms1p6>

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?

> 
> Cheers,
> MyungJoo
> 
> 

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

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-12 13:53 Sibi Sankar
     [not found] ` <CGME20181212135338epcas5p12f7a8cd1c7aab5d5c936cbc5c33eee07@epcms1p6>
2018-12-14  1:45   ` MyungJoo Ham
2019-02-19  5:12     ` Sibi Sankar [this message]
2019-03-04  8:21       ` Sibi Sankar
     [not found]       ` <CGME20181212135338epcas5p12f7a8cd1c7aab5d5c936cbc5c33eee07@epcms1p8>
2019-03-05  7:18         ` MyungJoo Ham
2019-03-06 17:44           ` Sibi Sankar

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