linux-kernel - Re: [PATCH v2 3/7] scsi: ufs: ufs-qcom: Allow the first init start with the maximum supported gear

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Message-ID: <f3bb9cf7-e57d-af5d-6516-9773ccb5dd1c@quicinc.com>
Date:   Wed, 8 Nov 2023 16:23:55 +0800
From:   Can Guo <quic_cang@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>,
        Can Guo <cang@....qualcomm.com>
CC:     <bvanassche@....org>, <stanley.chu@...iatek.com>,
        <adrian.hunter@...el.com>, <beanhuo@...ron.com>,
        <avri.altman@....com>, <junwoo80.lee@...sung.com>,
        <martin.petersen@...cle.com>, <linux-scsi@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/7] scsi: ufs: ufs-qcom: Allow the first init start
 with the maximum supported gear

Hi Mani,

On 11/8/2023 4:21 PM, Can Guo wrote:
> Hi Mani,
> 
> On 11/8/2023 1:23 PM, Manivannan Sadhasivam wrote:
>> On Mon, Nov 06, 2023 at 08:46:09PM -0800, Can Guo wrote:
>>> From: Can Guo <quic_cang@...cinc.com>
>>>
>>> During host driver init, the phy_gear is set to the minimum supported 
>>> gear
>>> (HS_G2). Then, during the first power mode change, the negotiated 
>>> gear, say
>>> HS-G4, is updated to the phy_gear variable so that in the second init 
>>> the
>>> updated phy_gear can be used to program the PHY.
>>>
>>> But the current code only allows update the phy_gear to a higher 
>>> value. If
>>> one wants to start the first init with the maximum support gear, say 
>>> HS-G4,
>>> the phy_gear is not updated to HS-G3 if the device only supports HS-G3.
>>>
>>
>> Can you elaborate when this can happen? AFAICS, there are 3 
>> possibilities of
>> initial phy gear with this series:
>>
>> 1. If ufshc is < 5.0, then G2 will be used.
>> 2. If ufshc is >= 5.0 and if the version is populated in register, 
>> then that
>> gear will be used. Most likely that gear can be G4/G5 depending on the 
>> device
>> connected.
>> 3. If ufshc is >=5.0 and version is not populated, then G4 will be used.
I think this made you confused, in case #3, HS-G5 is used as initial PHY 
gear, not G4 (in the last patch in this series).

Thanks,
Can Guo.
>>
>> In all the above cases, I do not see any necessity to switch the phy gear
>> setting to lower one while scaling. Since the gears are backwards 
>> compatible,
>> we always use one phy gear sequence. Moreover, we only have 2 init 
>> sequences.
>>
>> Please correct me if I'm missing anything.
>>
>> - Mani
> In the next patch, I am setting the initial PHY gear to max HS gear read
> from UFS host cap register, so that we don't need to keep updating the 
> initial value for host->phy_gear for different HW versions in future. 
> FYI, for HW ver 5 and 6, it is HS-G5. In future, the max gear might 
> become HS-G6 or higher on newer HW verions.
> 
> I the case #3, if HS-G5 is set to host->phy_gear, the first init uses 
> HS-G5, then after negotiation if the agreed gear is HS-G4, we need to 
> update host->phy_gear to HS-G4 (a lower value) such that we use a power 
> saving PHY gear settings during the 2nd init.
> 
> If the commit message is making you confused, I can update it in next 
> version. Please let me if I made any mistakes here.
> 
> Thanks,
> Can Guo.