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

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Message-ID: <20231128054522.GF3088@thinkpad>
Date:   Tue, 28 Nov 2023 11:15:22 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Can Guo <quic_cang@...cinc.com>
Cc:     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 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?

- 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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