linux-kernel - Re: [PATCH v18 1/2] scsi: ufs: Enable power management for wlun

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Message-ID: <9ae35c14-f8aa-a181-2259-2d32bd2c1f07@codeaurora.org>
Date:   Fri, 16 Apr 2021 11:21:48 -0700
From:   "Asutosh Das (asd)" <asutoshd@...eaurora.org>
To:     Bart Van Assche <bvanassche@....org>, cang@...eaurora.org,
        martin.petersen@...cle.com, adrian.hunter@...el.com,
        linux-scsi@...r.kernel.org
Cc:     linux-arm-msm@...r.kernel.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Bean Huo <beanhuo@...ron.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Yue Hu <huyue2@...ong.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Dinghao Liu <dinghao.liu@....edu.cn>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/SAMSUNG S3C, S5P AND EXYNOS ARM ARCHITECTURES" 
        <linux-samsung-soc@...r.kernel.org>,
        "moderated list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER..." 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v18 1/2] scsi: ufs: Enable power management for wlun

On 4/15/2021 4:11 PM, Bart Van Assche wrote:
> On 4/14/21 11:58 AM, Asutosh Das wrote:
>> [ ... ]
> 
Hi Bart,
Thanks for the comments. I will fix the comments in the next version.

> The following code is executed before ufshcd_async_scan() is called:
> 
> 	dev = hba->dev;
> 	[ ... ]
> 	/* Hold auto suspend until async scan completes */
> 	pm_runtime_get_sync(dev);
> 
That would only keep the hba runtime resumed. At this point of time the 
luns are not detected yet.
> and the following code occurs in ufshcd_add_lus():
> 
> 	pm_runtime_put_sync(hba->dev);
> 
> Isn't that sufficient to postpone enabling of runtime PM until LUN
> scanning has finished? Or in other words, is adding a
> pm_runtime_get_noresume() call in ufshcd_slave_configure() really necessary?
> 
Yes, because the supplier (device wlun) may be suspended otherwise in 
scsi_sysfs_add_sdev().
>> @@ -4979,15 +5035,9 @@ ufshcd_transfer_rsp_status(struct ufs_hba *hba, struct ufshcd_lrb *lrbp)
>>   			 */
>>   			if (!hba->pm_op_in_progress &&
>>   			    !ufshcd_eh_in_progress(hba) &&
>> -			    ufshcd_is_exception_event(lrbp->ucd_rsp_ptr) &&
>> -			    schedule_work(&hba->eeh_work)) {
>> -				/*
>> -				 * Prevent suspend once eeh_work is scheduled
>> -				 * to avoid deadlock between ufshcd_suspend
>> -				 * and exception event handler.
>> -				 */
>> -				pm_runtime_get_noresume(hba->dev);
>> -			}
>> +			    ufshcd_is_exception_event(lrbp->ucd_rsp_ptr))
>> +				/* Flushed in suspend */
>> +				schedule_work(&hba->eeh_work);
> 
> What makes it safe to leave out the above pm_runtime_get_noresume() call?
> 
The __ufshcd_wl_suspend() would flush this work so that it doesn't run 
after suspend.
> Thanks,
> 
> Bart.
> 


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