linux-kernel - Re: [PATCH 2/3] scsi: ufs: Keep device power on only fWriteBoosterBufferFlushDuringHibernate == 1

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Date:   Thu, 03 Dec 2020 12:45:00 +0100
From:   Bean Huo <huobean@...il.com>
To:     Avri Altman <Avri.Altman@....com>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] scsi: ufs: Keep device power on only
 fWriteBoosterBufferFlushDuringHibernate == 1

On Thu, 2020-12-03 at 10:46 +0000, Avri Altman wrote:
> > > > From: Bean Huo <beanhuo@...ron.com>
> > > > 
> > > > Keep device power mode as active power mode and VCC supply only
> > > > if
> > > > fWriteBoosterBufferFlushDuringHibernate setting 1 is
> > > > successful.
> > 
> > Hi Avri
> > Thanks so much taking time reiew.
> > 
> > > Why would it fail?
> > 
> > During the reliability testing in harsh environments, such as:
> > EMS testing, in the high/low-temperature environment. The system
> > would
> > reboot itself, there will be programming failure very likely.
> > If we assume failure will never hit, why we capture its result
> > following with dev_err(). If you keep using your phone in a harsh
> > environment, you will see this print message.
> > 
> > Of course, in a normal environment, the chance of failure likes you
> > to
> > win a lottery, but the possibility still exists.
> 
> Exactly.

so, you agree the possiblity of failure  exists.

> Hence we need-not any extra logic protecting device management
> command failures.

what extra logic? 

> 
> if reading the configuration pass correctly, and UFSHCD_CAP_WB_EN is
> set,


UFSHCD_CAP_WB_EN set is DRAM level. still in the cache.

> one should expect that any other functionality would work.
> 
No,  The programming will consume more power than reading, the
later setting will more possbile fail than reading.

> Otherwise, any non-standard behavior should be added with a quirk.
> 

NO, this is not what is standard or non-standard. This is independent
of UFS device/controller. It is a software design. IMO, we didn't deal
with programming status that is a potential bug. If having to impose to
a component, do you think should be controller or device? Instead of
addin a quirk, I prefer dropping this patch.




> Thanks,
> Avri
> > 
> > 
> > > Since UFSHCD_CAP_WB_EN is toggled off on ufshcd_wb_probe If the
> > > device doesn't support wb,
> > > The check ufshcd_is_wb_allowed should suffice, isn't it?
> > > 
> > 
> > No, UFSHCD_CAP_WB_EN only tells us if the platform supports WB,
> > doesn't tell us fWriteBoosterBufferFlushDuringHibernate status.
> > 
> > Thanks,
> > Bean