linux-kernel - Re: [PATCH v7 8/8] scsi: ufs: Select INITIAL adapt for HS Gear4

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Date:   Fri, 07 Feb 2020 13:10:35 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...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>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bean Huo <beanhuo@...ron.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bart Van Assche <bvanassche@....org>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Pedro Sousa <sousa@...opsys.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 8/8] scsi: ufs: Select INITIAL adapt for HS Gear4

On 2020-02-07 10:56, Can Guo wrote:
> On 2020-02-06 21:20, Avri Altman wrote:
>> Hi Can,
>> 
>> 
>>> ADAPT is added specifically for HS Gear4 mode only, select INITIAL 
>>> adapt
>>> before do power mode change to G4 and select no adapt before switch 
>>> to
>>> non-G4 modes.
>> 
>> UFSHCI 3.0 says:
>> 7.4.1 Adapt
>> The use of Adapt isn't mandatory but the specification provides some
>> guidelines on its use.
>> The HCI should perform an Initial Adapt in the following cases if the
>> link is running at HS-G4
>> speed:
>>  - If DME_RESET is initiated.
>>  - If an unused line is activated for HS-G4.
>>  - If UECDME.EC is triggered with bit 3 set to '1'.
>>  - If a change between Rate A and Rate B in HS-G4 is performed.
>> 
>> If it's not mandatory - why are we setting this for all vendors on all
>> platforms?
>> Or am I miss-reading the spec?
>> 
>> Thanks,
>> Avri
> 
> Hi Avri,
> 
> Yes, it is not mandatory, but I don't know a flash vendor that
> refuses to use ADAPT so far, it is even recommended by flash vendors.
> So there is no meaning of adding a specific quirk for it, as all flash
> vendors need this quirk. Otherwise, we would need to add another vops
> to allow platform vendors to control it before send PMC.
> 
> Any other suggestions?
> 
> FYI, ADAPT sequence is used to train an M-RX equalizer. It gives both
> sides better signal integrity against the influence caused by
> temperature and voltage variations. ADAPT is also used by Quality of
> Service Monitoring for HS-G4.
> 
> As for the usage of it, here is just setting the type of it before
> PMC to HS-G4, HW will use ADAPT, only if both sides support ADAPT,
> when it is required as what the spec is saying.
> 
> Thanks,
> 
> Can Guo.

Hi Avri,

I will drop this one for now as it may take some time to nail down it.
I will come back with a separate patch series for it later.

Thanks for the review.

Can Guo.