linux-kernel - Re: [PATCH v12 1/2] scsi: ufs: Enable power management for wlun

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Message-ID: <45101050-83de-6488-7b17-271e0acea87b@codeaurora.org>
Date:   Fri, 19 Mar 2021 08:08:35 -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>,
        Bean Huo <beanhuo@...ron.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Lee Jones <lee.jones@...aro.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Dinghao Liu <dinghao.liu@....edu.cn>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        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 v12 1/2] scsi: ufs: Enable power management for wlun

On 3/18/2021 8:12 PM, Bart Van Assche wrote:
> On 3/18/21 5:35 PM, Asutosh Das wrote:
>> During runtime-suspend of ufs host, the scsi devices are
>> already suspended and so are the queues associated with them.
>> But the ufs host sends SSU to wlun during its runtime-suspend.
>> During the process blk_queue_enter checks if the queue is not in
>> suspended state. If so, it waits for the queue to resume, and never
>> comes out of it.
>> The commit
>> (d55d15a33: scsi: block: Do not accept any requests while suspended)
>> adds the check if the queue is in suspended state in blk_queue_enter().
> 
Hi Bart,
Thanks for the review comments.

> What is the role of the WLUN during runtime suspend and why does a
> command need to be sent to the WLUN during runtime suspend? Although it
> is possible to derive this from the source code, please explain this in
> the patch description.
> 
Ok. Will explain it in the next version.

> What does the acronym SSU stand for? This doesn't seem like a commonly
> used kernel acronym to me so please expand that acronym.
>
START STOP UNIT.
Anyway, I'll expand it in the next version.

>> Fix this by registering ufs device wlun as a scsi driver and
>> registering it for block runtime-pm. Also make this as a
>> supplier for all other luns. That way, this device wlun
>> suspends after all the consumers and resumes after
>> hba resumes.
> 
> That's an interesting solution.
> 
>> -void __exit ufs_debugfs_exit(void)
>> +void ufs_debugfs_exit(void)
> 
> Is the above change related to the rest of this patch?
> 
Yes, it's used to handle an error in ufshcd_core_init() function.

>>   static struct platform_driver ufs_qcom_pltform = {
>> diff --git a/drivers/scsi/ufs/ufs_bsg.c b/drivers/scsi/ufs/ufs_bsg.c
>> index 5b2bc1a..cbb5a90 100644
>> --- a/drivers/scsi/ufs/ufs_bsg.c
>> +++ b/drivers/scsi/ufs/ufs_bsg.c
>> @@ -97,7 +97,7 @@ static int ufs_bsg_request(struct bsg_job *job)
>>   
>>   	bsg_reply->reply_payload_rcv_len = 0;
>>   
>> -	pm_runtime_get_sync(hba->dev);
>> +	scsi_autopm_get_device(hba->sdev_ufs_device);
> 
> Can the pm_runtime_get_sync() to scsi_autopm_get_device() changes be
> moved into a separate patch?
>
I guess so. But then this patch would have issues when used independently.

>> +static inline bool is_rpmb_wlun(struct scsi_device *sdev)
>> +{
>> +	return (sdev->lun == ufshcd_upiu_wlun_to_scsi_wlun(UFS_UPIU_RPMB_WLUN));
>> +}
> 
> Has this patch been verified with checkpatch? Checkpatch should have
> reported the following for the above code:
> 
> 	return is not a function, parentheses are not required
> 
Yes, it has been verified. But I didn't see any error reports.
Below is the o/p of checkpatch:

$ ./scripts/checkpatch.pl /tmp/up/ufs-pm-v12/*
------------------------------------------
/tmp/up/ufs-pm-v12/0000-cover-letter.patch
------------------------------------------
WARNING: Possible unwrapped commit description (prefer a maximum 75 
chars per line)
#107:
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project.

total: 0 errors, 1 warnings, 0 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
       mechanically convert to the typical style using --fix or 
--fix-inplace.

/tmp/up/ufs-pm-v12/0000-cover-letter.patch has style problems, please 
review.
-----------------------------------------------------------------------
/tmp/up/ufs-pm-v12/0001-scsi-ufs-Enable-power-management-for-wlun.patch
-----------------------------------------------------------------------
total: 0 errors, 0 warnings, 1180 lines checked

/tmp/up/ufs-pm-v12/0001-scsi-ufs-Enable-power-management-for-wlun.patch 
has no obvious style problems and is ready for submission.
---------------------------------------------------------------------
/tmp/up/ufs-pm-v12/0002-ufs-sysfs-Resume-the-proper-scsi-device.patch
---------------------------------------------------------------------
total: 0 errors, 0 warnings, 91 lines checked

/tmp/up/ufs-pm-v12/0002-ufs-sysfs-Resume-the-proper-scsi-device.patch 
has no obvious style problems and is ready for submission.

NOTE: If any of the errors are false positives, please report
       them to the maintainer, see CHECKPATCH in MAINTAINERS.


>> +static inline bool is_device_wlun(struct scsi_device *sdev)
>> +{
>> +	return (sdev->lun ==
>> +		ufshcd_upiu_wlun_to_scsi_wlun(UFS_UPIU_UFS_DEVICE_WLUN));
>> +}
> 
> Same comment here.
> 
>>   		/*
>> -		 * Don't assume anything of pm_runtime_get_sync(), if
>> +		 * Don't assume anything of resume, if
>>   		 * resume fails, irq and clocks can be OFF, and powers
>>   		 * can be OFF or in LPM.
>>   		 */
> 
> Please make better use of the horizontal space in the above comment by
> making comment lines longer.
> 
Ok Sure.

> Thanks,
> 
> Bart.
> 

-asd

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