linux-kernel - Re: [PATCH RFC v1 1/1] scsi: pm: Leave runtime resume along if block layer PM is enabled

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Date:   Wed, 18 Nov 2020 16:49:47 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        Stanley Chu <stanley.chu@...iatek.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH RFC v1 1/1] scsi: pm: Leave runtime resume along if block
 layer PM is enabled

Hi Bart,

On 2020-11-18 12:38, Bart Van Assche wrote:
> On 11/15/20 5:42 PM, Can Guo wrote:
>> Actually, I am thinking about removing all the pm_runtime_set_active()
>> codes in both scsi_bus_resume_common() and scsi_dev_type_resume() - we
>> don't need to forcibly set the runtime PM status to RPM_ACTIVE for 
>> either
>> SCSI host/target or SCSI devices.
>> 
>> Whenever we access one SCSI device, either block layer or somewhere in
>> the path (e.g. throgh sg IOCTL, sg_open() calls 
>> scsi_autopm_get_device())
>> should runtime resume the device first, and the runtime PM framework 
>> makes
>> sure device's parent (and its parent's parent and so on)gets resumed 
>> as
>> well.
>> Thus, the pm_runtime_set_active() seems redundant. What do you think?
> 
> Hi Can,
> 
> It is not clear to me why the pm_runtime_set_active() calls occur in 
> the
> scsi_pm.c source file since the block layer automatically activates
> block devices if necessary. Maybe these calls are a leftover from a 
> time
> when runtime suspended devices were not resumed automatically by the
> block layer? Anyway, I'm fine with removing these calls.
> 
> Thanks,
> 
> Bart.

Yes, I agree with you. Let me test the new patch (which removes all the
pm_runtime_set_active() calls) first, if no issue found, I will upload
it for review.

Thanks,

Can Guo.