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: <20231109034717.GD3752@thinkpad>
Date:   Thu, 9 Nov 2023 09:17:17 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Can Guo <quic_cang@...cinc.com>
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

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.

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().

- Mani

> Thanks,
> Can Guo.

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