linux-kernel - Re: [PATCH v1 1/2] scsi: ufs: set device as default active power mode during initialization only

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Date:   Thu, 2 Jan 2020 14:38:44 +0800
From:   Stanley Chu <stanley.chu@...iatek.com>
To:     Can Guo <cang@...eaurora.org>
CC:     <martin.petersen@...cle.com>, <linux-scsi@...r.kernel.org>,
        <andy.teng@...iatek.com>, <jejb@...ux.ibm.com>,
        <chun-hung.wu@...iatek.com>, <kuohong.wang@...iatek.com>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        <asutoshd@...eaurora.org>, <avri.altman@....com>,
        <linux-mediatek@...ts.infradead.org>, <peter.wang@...iatek.com>,
        <linux-scsi-owner@...r.kernel.org>, <subhashj@...eaurora.org>,
        <alim.akhtar@...sung.com>, <beanhuo@...ron.com>,
        <pedrom.sousa@...opsys.com>, <bvanassche@....org>,
        <linux-arm-kernel@...ts.infradead.org>, <matthias.bgg@...il.com>,
        <ron.hsu@...iatek.com>, <cc.chou@...iatek.com>
Subject: Re: [PATCH v1 1/2] scsi: ufs: set device as default active power
 mode during initialization only

Hi Can,

On Tue, 2019-12-31 at 16:35 +0800, Can Guo wrote:

> Hi Stanley,
> 
> I missed this mail before I hit send. In current code, as per my 
> understanding,
> UFS device's power state should be Active after ufshcd_link_startup() 
> returns.
> If I am wrong, please feel free to correct me.
> 

Yes, this assumption of ufshcd_probe_hba() is true so I will drop this
patch.
Thanks for remind.

> Due to you are almost trying to revert commit 7caf489b99a42a, I am just 
> wondering
> if you encounter failure/error caused by it.

Yes, we actually have some doubts from the commit message of "scsi: ufs:
issue link startup 2 times if device isn't active"

If we configured system suspend as device=PowerDown/Link=LinkDown mode,
during resume, the 1st link startup will be successful, and after that
device could be accessed normally so it shall be already in Active power
mode. We did not find devices which need twice linkup for normal work.

And because the 1st linkup is OK, the forced 2nd linkup by commit "scsi:
ufs: issue link startup 2 times if device isn't active" leads to link
lost and finally the 3rd linkup is made again by retry mechanism in
ufshcd_link_startup() and be successful. So a linkup performance issue
is introduced here: We actually need one-time linkup only but finally
got 3 linkup operations.

According to the UFS spec, all reset types (including POR and Host
UniPro Warm Reset which both may happen in above configurations) other
than LU reset, UFS device power mode shall return to Sleep mode or
Active mode depending on bInitPowerMode, by default, it's Active mode.

So we are curious that why enforcing twice linkup is necessary here?
Could you kindly help us clarify this?

If anything wrong in above description, please feel free to correct me.

> 
> Happy new year to you too!
> 
> Thanks,
> 
> Can Guo

Thanks,

Stanley

> 
> _______________________________________________
> Linux-mediatek mailing list
> Linux-mediatek@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-mediatek

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