From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sibi Sankar Subject: Re: [PATCH v4] PM / devfreq: Restart previous governor if new governor fails to start Date: Mon, 04 Mar 2019 13:51:53 +0530 Message-ID: <946aa4e13aec4f84e6ae2d91e772fb1f@codeaurora.org> References: <20181212135313.30268-1-sibis@codeaurora.org> <20181214014527epcms1p6c783b4cd1602bbcbcb6e725f840db479@epcms1p6> <39d3a906-b734-9bb8-c60a-48948bb21338@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <39d3a906-b734-9bb8-c60a-48948bb21338@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: myungjoo.ham@samsung.com, Kyungmin Park Cc: Chanwoo Choi , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm-owner@vger.kernel.org, skannan@codeaurora.org List-Id: linux-pm@vger.kernel.org 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 >>> >>> 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 >>> Signed-off-by: Saravana Kannan >>> Reviewed-by: Chanwoo Choi >> >> 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 >> >> -- -- Sibi Sankar -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.