linux-kernel - Re: [PATCH v3] scsi: ufs: Cleanup completed request without interrupt notification

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Message-ID: <1594607245.22878.8.camel@mtkswgap22>
Date:   Mon, 13 Jul 2020 10:27:25 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Bart Van Assche <bvanassche@....org>
CC:     <linux-scsi@...r.kernel.org>, <martin.petersen@...cle.com>,
        <avri.altman@....com>, <alim.akhtar@...sung.com>,
        <jejb@...ux.ibm.com>, <beanhuo@...ron.com>,
        <asutoshd@...eaurora.org>, <cang@...eaurora.org>,
        <matthias.bgg@...il.com>, <linux-mediatek@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kuohong.wang@...iatek.com>,
        <peter.wang@...iatek.com>, <chun-hung.wu@...iatek.com>,
        <andy.teng@...iatek.com>, <chaotian.jing@...iatek.com>,
        <cc.chou@...iatek.com>
Subject: Re: [PATCH v3] scsi: ufs: Cleanup completed request without
 interrupt notification

Hi Bart and Avri,

On Sun, 2020-07-12 at 18:39 -0700, Bart Van Assche wrote:
> On 2020-07-06 06:21, Stanley Chu wrote:
> > If somehow no interrupt notification is raised for a completed request
> > and its doorbell bit is cleared by host, UFS driver needs to cleanup
> > its outstanding bit in ufshcd_abort().
> 
> How is it possible that no interrupt notification is raised for a completed
> request? Is this the result of a hardware shortcoming or rather the result
> of how the UFS driver works? In the latter case, is this patch perhaps a
> workaround? If so, has it been considered to fix the root cause instead of
> implementing a workaround?

Actually this fail is triggered by "error injection" to produce a
command timeout event for checking if anything can be improved or fixed.

I agree that "no interrupt notification" may be something wrong in
hardware and the root cause shall be fixed in the highest priority.
However from this injection, we found ufshcd_abort() indeed has a defect
flow for a corner case, so we are looking for the solution to fix the
"hole".

What would you think if Linux driver shall consider this case? If this
is not necessary, I would drop this patch : )

Thanks a lot,
Stanley Chu

> 
> In section 7.2.3 of the UFS specification I found the following about how
> to process request completions: "Software determines if new TRs have
> completed since step #2, by repeating one of the two methods described in
> step #2. If new TRs have completed, software repeats the sequence from step
> #3." Is such a loop perhaps missing from the Linux UFS driver?
> 
> Thanks,
> 
> Bart.