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: Tue, 19 Feb 2019 10:42:01 +0530 Message-ID: <39d3a906-b734-9bb8-c60a-48948bb21338@codeaurora.org> References: <20181212135313.30268-1-sibis@codeaurora.org> <20181214014527epcms1p6c783b4cd1602bbcbcb6e725f840db479@epcms1p6> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181214014527epcms1p6c783b4cd1602bbcbcb6e725f840db479@epcms1p6> Content-Language: en-US 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, 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 > > -- Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc, is a member of Code Aurora Forum, a Linux Foundation Collaborative Project