linux-kernel - Re: [EXT] [PATCH v1 5/5] scsi: ufs: Complete pending requests in host reset and restore path

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Message-ID: <0dc202a1decb6bbc103253b8c3c8c8ce@codeaurora.org>
Date:   Thu, 14 Nov 2019 09:03:10 +0800
From:   cang@...eaurora.org
To:     "Bean Huo (beanhuo)" <beanhuo@...ron.com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Subhash Jadavani <subhashj@...eaurora.org>,
        Tomas Winkler <tomas.winkler@...el.com>,
        open list <linux-kernel@...r.kernel.org>,
        Can Guo <cang@...eaurora.org>
Subject: Re: [EXT] [PATCH v1 5/5] scsi: ufs: Complete pending requests in host
 reset and restore path

On 2019-11-14 06:04, Bean Huo (beanhuo) wrote:
>> 
>> In UFS host reset and restore path, before probe, we stop and start 
>> the host
>> controller once. After host controller is stopped, the pending 
>> requests, if any,
>> are cleared from the doorbell, but no completion IRQ would be raised 
>> due to the
>> hba is stopped.
>> These pending requests shall be completed along with the first NOP_OUT
>> command(as it is the first command which can raise a transfer 
>> completion
>> IRQ) sent during probe.
> 
> Hi, Can
> I am not sure for this point, because there is HW/SW device reset
> before or after host reset/restore.
> Device HW/SW reset also will clear the pended tasks in device side.
> That will be better.
> I think Qcom platform already enabled HW reset.
> 
> //Bean
> 

Hi Bean,

By pending tasks here, it means the requests sent down from scsi/block 
layer,
but have not yet been handled by ufs driver(cmd->scsi_done() have not 
been called yet for these requests).
For these requests, although removed by host and UFS device in their HW 
queues(doorbell),
UFS driver still needs to complete them from SW side(call 
cmd->scsi_done() for each one of them) to
let upper layer know that they are finished(although not successfully) 
to avoid hitting
timeout of these pending tasks. I hope I make my explanation clearly.

Best Regards,
Can Guo.

>> Since the OCSs of these pending requests are not SUCCESS(because they 
>> are not
>> yet literally finished), their UPIUs shall be dumped. When there are 
>> multiple
>> pending requests, the UPIU dump can be overwhelming and may lead to 
>> stability
>> issues because it is in atomic context.
>> Therefore, before probe, complete these pending requests right after 
>> host
>> controller is stopped.