linux-kernel - Re: [PATCH 1/3] ufs: ufs-qcom: Add support for DT-based gear and rate limiting

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Message-ID: <fl4t5fpyd5o535djn3f5vbq4lqqtwx2dzcphxfdf7s6kxedcsb@yz65chgbcgd3>
Date: Thu, 31 Jul 2025 20:43:30 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
Cc: mani@...nel.org, alim.akhtar@...sung.com, avri.altman@....com,
        bvanassche@....org, robh@...nel.org, krzk+dt@...nel.org,
        conor+dt@...nel.org, andersson@...nel.org, konradybcio@...nel.org,
        James.Bottomley@...senpartnership.com, martin.petersen@...cle.com,
        agross@...nel.org, linux-arm-msm@...r.kernel.org,
        linux-scsi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ufs: ufs-qcom: Add support for DT-based gear and
 rate limiting

On Thu, Jul 31, 2025 at 09:58:47PM +0530, Ram Kumar Dwivedi wrote:
> 
> 
> On 24-Jul-25 2:11 PM, Dmitry Baryshkov wrote:
> > On Thu, 24 Jul 2025 at 10:35, Ram Kumar Dwivedi
> > <quic_rdwivedi@...cinc.com> wrote:
> >>
> >>
> >>
> >> On 23-Jul-25 12:24 AM, Dmitry Baryshkov wrote:
> >>> On Tue, Jul 22, 2025 at 09:41:01PM +0530, Ram Kumar Dwivedi wrote:
> >>>> Add optional device tree properties to limit Tx/Rx gear and rate during UFS
> >>>> initialization. Parse these properties in ufs_qcom_init() and apply them to
> >>>> host->host_params to enforce platform-specific constraints.
> >>>>
> >>>> Use this mechanism to cap the maximum gear or rate on platforms with
> >>>> hardware limitations, such as those required by some automotive customers
> >>>> using SA8155. Preserve the default behavior if the properties are not
> >>>> specified in the device tree.
> >>>>
> >>>> Signed-off-by: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
> >>>> ---
> >>>>  drivers/ufs/host/ufs-qcom.c | 28 ++++++++++++++++++++++------
> >>>>  1 file changed, 22 insertions(+), 6 deletions(-)
> >>>>
> >>>> diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
> >>>> index 4bbe4de1679b..5e7fd3257aca 100644
> >>>> --- a/drivers/ufs/host/ufs-qcom.c
> >>>> +++ b/drivers/ufs/host/ufs-qcom.c
> >>>> @@ -494,12 +494,8 @@ static int ufs_qcom_power_up_sequence(struct ufs_hba *hba)
> >>>>       * If the HS-G5 PHY gear is used, update host_params->hs_rate to Rate-A,
> >>>>       * so that the subsequent power mode change shall stick to Rate-A.
> >>>>       */
> >>>> -    if (host->hw_ver.major == 0x5) {
> >>>> -            if (host->phy_gear == UFS_HS_G5)
> >>>> -                    host_params->hs_rate = PA_HS_MODE_A;
> >>>> -            else
> >>>> -                    host_params->hs_rate = PA_HS_MODE_B;
> >>>> -    }
> >>>> +    if (host->hw_ver.major == 0x5 && host->phy_gear == UFS_HS_G5)
> >>>> +            host_params->hs_rate = PA_HS_MODE_A;
> >>>
> >>> Why? This doesn't seem related.
> >>
> >> Hi Dmitry,
> >>
> >> I have refactored the patch to put this part in a separate patch in latest patchset.
> >>
> >> Thanks,
> >> Ram.
> >>
> >>>
> >>>>
> >>>>      mode = host_params->hs_rate == PA_HS_MODE_B ? PHY_MODE_UFS_HS_B : PHY_MODE_UFS_HS_A;
> >>>>
> >>>> @@ -1096,6 +1092,25 @@ static void ufs_qcom_set_phy_gear(struct ufs_qcom_host *host)
> >>>>      }
> >>>>  }
> >>>>
> >>>> +static void ufs_qcom_parse_limits(struct ufs_qcom_host *host)
> >>>> +{
> >>>> +    struct ufs_host_params *host_params = &host->host_params;
> >>>> +    struct device_node *np = host->hba->dev->of_node;
> >>>> +    u32 hs_gear, hs_rate = 0;
> >>>> +
> >>>> +    if (!np)
> >>>> +            return;
> >>>> +
> >>>> +    if (!of_property_read_u32(np, "limit-hs-gear", &hs_gear)) {
> >>>
> >>> These are generic properties, so they need to be handled in a generic
> >>> code path.
> >>
> >> Hi Dmitry,
> >>
> >>
> >> Below is the probe path for the UFS-QCOM platform driver:
> >>
> >> ufs_qcom_probe
> >>   └─ ufshcd_platform_init
> >>        └─ ufshcd_init
> >>             └─ ufs_qcom_init
> >>                  └─ ufs_qcom_set_host_params
> >>                       └─ ufshcd_init_host_params (initialized with default values)
> >>                            └─ ufs_qcom_get_hs_gear (overrides gear based on controller capability)
> >>                                 └─ ufs_qcom_set_phy_gear (further overrides based on controller limitations)
> >>
> >>
> >> The reason I added the logic in ufs-qcom.c is that even if it's placed in ufshcd-platform.c, the values get overridden in ufs-qcom.c.
> >> If you prefer, I can move the parsing logic API to ufshcd-platform.c but still it needs to be called from ufs-qcom.c.
> > 
> > I was thinking about ufshcd_init() or similar function.
> Hi Dmitry,
> 
> It appears we can't move the logic to ufshcd.c because the PHY is initialized in ufs-qcom.c, and the gear must be set during that initialization.
> 
> Limiting the gear and lane in ufshcd.c won’t be effective, as qcom_init sets the PHY to the maximum supported gear by default. As a result, the PHY would still initialize with the max gear, defeating the purpose of the limits.
> 
> To ensure the PHY is initialized with the intended gear, the limits needs to be applied directly in ufs_qcom.c

The limits are to be applied in ufs_qcom.c, but they can (and should) be
parsed in the generic code.

> 
> Please let me know if you have any concerns.
> 
> Thanks,
> Ram.
> 
> 
> > 
> >>
> >> Thanks,
> >> Ram.
> >>
> >>
> >>>
> >>> Also, the patch with bindings should preceed driver and DT changes.
> >>
> >> Hi Dmitry,
> >>
> >> I have reordered the patch series to place the DT binding change as the first patch in latest patchset.
> >>
> >> Thanks,
> >> Ram.
> >>
> >>
> >>>
> >>>> +            host_params->hs_tx_gear = hs_gear;
> >>>> +            host_params->hs_rx_gear = hs_gear;
> >>>> +            host->phy_gear = hs_gear;
> >>>> +    }
> >>>> +
> >>>> +    if (!of_property_read_u32(np, "limit-rate", &hs_rate))
> >>>> +            host_params->hs_rate = hs_rate;
> >>>> +}
> >>>> +
> >>>>  static void ufs_qcom_set_host_params(struct ufs_hba *hba)
> >>>>  {
> >>>>      struct ufs_qcom_host *host = ufshcd_get_variant(hba);
> >>>> @@ -1337,6 +1352,7 @@ static int ufs_qcom_init(struct ufs_hba *hba)
> >>>>      ufs_qcom_advertise_quirks(hba);
> >>>>      ufs_qcom_set_host_params(hba);
> >>>>      ufs_qcom_set_phy_gear(host);
> >>>> +    ufs_qcom_parse_limits(host);
> >>>>
> >>>>      err = ufs_qcom_ice_init(host);
> >>>>      if (err)
> >>>> --
> >>>> 2.50.1
> >>>>
> >>>
> >>
> > 
> > 
> 

-- 
With best wishes
Dmitry