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

From: Bean Huo <huobean@gmail.com>
To: Avri Altman <Avri.Altman@wdc.com>,
	"alim.akhtar@samsung.com" <alim.akhtar@samsung.com>,
	"asutoshd@codeaurora.org" <asutoshd@codeaurora.org>,
	"jejb@linux.ibm.com" <jejb@linux.ibm.com>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"stanley.chu@mediatek.com" <stanley.chu@mediatek.com>,
	"beanhuo@micron.com" <beanhuo@micron.com>,
	"bvanassche@acm.org" <bvanassche@acm.org>,
	"tomas.winkler@intel.com" <tomas.winkler@intel.com>,
	"cang@codeaurora.org" <cang@codeaurora.org>
Cc: "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] scsi: ufs: Keep device power on only fWriteBoosterBufferFlushDuringHibernate == 1
Date: Thu, 03 Dec 2020 12:45:00 +0100	[thread overview]
Message-ID: <2578a5fa2323f46b29dc8808b948ed5eaea6fbca.camel@gmail.com> (raw)
In-Reply-To: <DM6PR04MB657551290696C7EBD8339328FCF20@DM6PR04MB6575.namprd04.prod.outlook.com>

On Thu, 2020-12-03 at 10:46 +0000, Avri Altman wrote:
> > > > From: Bean Huo <beanhuo@micron.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