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

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Message-ID: <bc69d9ef-6ddc-4389-8bf0-9405385a494b@quicinc.com>
Date:   Tue, 28 Nov 2023 16:05:59 +0800
From:   Can Guo <quic_cang@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>
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

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. 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.

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
>>
>