linux-kernel - Re: [PATCH RFC] scsi: ufs: Disable blk-mq for now

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Message-ID: <e4d0c716-006a-72cb-0240-4ae5749b21b8@intel.com>
Date:   Thu, 13 Sep 2018 15:15:39 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Bart Van Assche <Bart.VanAssche@....com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stanislav Nijnikov <stanislav.nijnikov@....com>,
        Evan Green <evgreen@...omium.org>,
        Vinayak Holikatti <vinholikatti@...il.com>,
        Janek Kotas <jank@...ence.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Subhash Jadavani <subhashj@...eaurora.org>,
        Sayali Lokhande <sayalil@...eaurora.org>,
        Li Wei <liwei213@...wei.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Alex Lemberg <Alex.Lemberg@...disk.com>
Subject: Re: [PATCH RFC] scsi: ufs: Disable blk-mq for now

On 13/09/18 15:05, Ming Lei wrote:
> On Thu, Sep 13, 2018 at 02:28:48PM +0300, Adrian Hunter wrote:
>> blk-mq does not support runtime pm, so disable blk-mq support for now.
> 
> So could you describe a bit what the issue you are trying to fix?

UFS is a low-power solution, so we must be able to runtime suspend.

> 
> This is host level runtime PM you are trying to address, and if blk-mq
> runtime isn't enabled, I guess the host won't be runtime suspended at all
> because some of its descendant are always active.
> 
> So seems we need to do nothing for preventing the host controller from
> entering runtime suspend.

We don't want to prevent the host controller from runtime suspending, quite
the opposite.