linux-kernel - Re: [PATCH v5 04/10] scsi: ufs: ufs-qcom: Limit negotiated gear to selected PHY gear

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Message-ID: <20231128105237.GN3088@thinkpad>
Date:   Tue, 28 Nov 2023 16:22:37 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Can Guo <quic_cang@...cinc.com>
Cc:     Manivannan Sadhasivam <mani@...nel.org>, bvanassche@....org,
        adrian.hunter@...el.com, beanhuo@...ron.com, avri.altman@....com,
        junwoo80.lee@...sung.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-arm-msm@...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 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 04/10] scsi: ufs: ufs-qcom: Limit negotiated gear to
 selected PHY gear

On Tue, Nov 28, 2023 at 04:05:59PM +0800, Can Guo wrote:
> Hi Mani,
> 
> On 11/28/2023 1:45 PM, Manivannan Sadhasivam wrote:
> > On Thu, Nov 23, 2023 at 12:46:24AM -0800, Can Guo wrote:
> > > In the dual init scenario, the initial PHY gear is set to HS-G2, and the
> > > first Power Mode Change (PMC) is meant to find the best matching PHY gear
> > > for the 2nd init. However, for the first PMC, if the negotiated gear (say
> > > HS-G4) is higher than the initial PHY gear, we cannot go ahead let PMC to
> > > the negotiated gear happen, because the programmed UFS PHY settings may not
> > > support the negotiated gear. Fix it by overwriting the negotiated gear with
> > > the PHY gear.
> > > 
> > 
> > I don't quite understand this patch. If the phy_gear is G2 initially and the
> > negotiated gear is G4, then as per this change,
> > 
> > phy_gear = G4;
> > negotiated gear = G2;
> > 
> > Could you please explain how this make sense?
> 
> phy_gear was G2 (in the beginning) and just now changed to G4, but the PHY
> settings programmed in the beginning can only support no-G4 (not G4).
> Without this change, as the negotiated gear is G4, the power mode change is
> going to put UFS at HS-G4 mode, but the PHY settings programmed is no-G4.

But we are going to reinit the PHY anyway, isn't it?

> This change is to limit the negotiated gear to HS-G2 for the 1st init. In
> the 2nd init, as the new PHY gear is G4, G4 PHY settings would be
> programmed, it'd be safe to put the UFS at HS-G4 mode.
> 

Why do we need to limit it since we already have the logic in place to set
whatever gear mode applicable for 1st init?

- Mani

> Thanks,
> Can Guo.
> > 
> > - Mani
> > 
> > > Signed-off-by: Can Guo <quic_cang@...cinc.com>
> > > ---
> > >   drivers/ufs/host/ufs-qcom.c | 7 ++++++-
> > >   1 file changed, 6 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
> > > index cc0eb37..d4edf58 100644
> > > --- a/drivers/ufs/host/ufs-qcom.c
> > > +++ b/drivers/ufs/host/ufs-qcom.c
> > > @@ -920,8 +920,13 @@ static int ufs_qcom_pwr_change_notify(struct ufs_hba *hba,
> > >   		 * because, the PHY gear settings are backwards compatible and we only need to
> > >   		 * change the PHY gear settings while scaling to higher gears.
> > >   		 */
> > > -		if (dev_req_params->gear_tx > host->phy_gear)
> > > +		if (dev_req_params->gear_tx > host->phy_gear) {
> > > +			u32 old_phy_gear = host->phy_gear;
> > > +
> > >   			host->phy_gear = dev_req_params->gear_tx;
> > > +			dev_req_params->gear_tx = old_phy_gear;
> > > +			dev_req_params->gear_rx = old_phy_gear;
> > > +		}
> > >   		/* enable the device ref clock before changing to HS mode */
> > >   		if (!ufshcd_is_hs_mode(&hba->pwr_info) &&
> > > -- 
> > > 2.7.4
> > > 
> > 

-- 
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