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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Date:   Thu, 9 Nov 2023 12:07:37 +0800
From:   Can Guo <quic_cang@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>
CC:     Can Guo <cang@....qualcomm.com>, <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 11/9/2023 11:47 AM, Manivannan Sadhasivam wrote:
> On Wed, Nov 08, 2023 at 04:21:52PM +0800, 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.
>>>
>>> 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.
>>
> 
> I see redundancy while setting the phy_gear and it is leading to confusion.
> In ufs_qcom_set_host_params(), first you are setting phy_gear based on
> ufs_qcom_get_hs_gear(), then changing it again with the version check for v5.
> 
> I don't see a necessity for "host->phy_gear = host_params->hs_tx_gear", since in
> the later check, you are covering both version <5 and >=5.
In the case of HW version >= 5, we are only overwriting the PHY gear 
only if the UFS device cannot support HS-G5. Hence, we need to give 
host->phy_gear an initial value.

> 
> Btw, it would be better to move this logic to a separate function like
> ufs_qcom_get_phy_gear() to align with ufs_qcom_get_hs_gear().
> 
OK, will do in next version.

Thanks,
Can Guo.
> - Mani
> 
>> Thanks,
>> Can Guo.
>