linux-kernel - Re: [PATCH V5 3/4] ufs: pltfrm: Allow limiting HS gear and rate via DT

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Message-ID: <3b2d0e8b-8d19-474d-91f8-d9195e1284fa@quicinc.com>
Date: Wed, 17 Sep 2025 19:44:37 +0530
From: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
To: Alim Akhtar <alim.akhtar@...sung.com>, <avri.altman@....com>,
        <bvanassche@....org>, <robh@...nel.org>, <krzk+dt@...nel.org>,
        <conor+dt@...nel.org>, <mani@...nel.org>,
        <James.Bottomley@...senPartnership.com>, <martin.petersen@...cle.com>
CC: <linux-scsi@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        "'Nitin
 Rawat'" <quic_nitirawa@...cinc.com>
Subject: Re: [PATCH V5 3/4] ufs: pltfrm: Allow limiting HS gear and rate via
 DT



On 03-Sep-25 9:58 AM, Alim Akhtar wrote:
> 
> 
>> -----Original Message-----
>> From: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
>> Sent: Tuesday, September 2, 2025 10:19 PM
>> To: alim.akhtar@...sung.com; avri.altman@....com;
>> bvanassche@....org; robh@...nel.org; krzk+dt@...nel.org;
>> conor+dt@...nel.org; mani@...nel.org;
>> James.Bottomley@...senPartnership.com; martin.petersen@...cle.com
>> Cc: linux-scsi@...r.kernel.org; devicetree@...r.kernel.org; linux-
>> kernel@...r.kernel.org; linux-arm-msm@...r.kernel.org; Nitin Rawat
>> <quic_nitirawa@...cinc.com>
>> Subject: [PATCH V5 3/4] ufs: pltfrm: Allow limiting HS gear and rate via
> DT
>>
>> Add support for parsing 'limit-hs-gear' and 'limit-rate' device tree
> properties
>> to restrict high-speed gear and rate during initialization.
>>
>> This is useful in cases where the customer board may have signal
> integrity,
>> clock configuration or layout issues that prevent reliable operation at
> higher
>> gears. Such limitations are especially critical in those platforms, where
>> stability is prioritized over peak performance.
>>
>> Co-developed-by: Nitin Rawat <quic_nitirawa@...cinc.com>
>> Signed-off-by: Nitin Rawat <quic_nitirawa@...cinc.com>
>> Signed-off-by: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
>> ---
>>  drivers/ufs/host/ufshcd-pltfrm.c | 36
>> ++++++++++++++++++++++++++++++++  drivers/ufs/host/ufshcd-pltfrm.h
>> |  1 +
>>  2 files changed, 37 insertions(+)
>>
>> diff --git a/drivers/ufs/host/ufshcd-pltfrm.c b/drivers/ufs/host/ufshcd-
>> pltfrm.c
>> index ffe5d1d2b215..4df6885f0dc0 100644
>> --- a/drivers/ufs/host/ufshcd-pltfrm.c
>> +++ b/drivers/ufs/host/ufshcd-pltfrm.c
>> @@ -430,6 +430,42 @@ int ufshcd_negotiate_pwr_params(const struct
>> ufs_host_params *host_params,  }
>> EXPORT_SYMBOL_GPL(ufshcd_negotiate_pwr_params);
>>
>> +/**
>> + * ufshcd_parse_limits - Parse DT-based gear and rate limits for UFS
>> + * @hba: Pointer to UFS host bus adapter instance
>> + * @host_params: Pointer to UFS host parameters structure to be updated
>> + *
>> + * This function reads optional device tree properties to apply
>> + * platform-specific constraints.
>> + *
>> + * "limit-hs-gear": Specifies the max HS gear.
>> + * "limit-rate": Specifies the max High-Speed rate.
>> + */
>> +void ufshcd_parse_limits(struct ufs_hba *hba, struct ufs_host_params
> 
> May be s/ufshcd_parse_limits/ ufshcd_parse_gear_limits()
> 
> "Limits" is very generic and also not aligning with the property names.
> Also suggest to change limit-rate to limit-gear-rate.

Hi Alim,

I have addressed this in next patchset.

> 
>> +*host_params) {
>> +	struct device_node *np = hba->dev->of_node;
>> +	u32 hs_gear;
>> +	const char *hs_rate;
>> +
>> +	if (!np)
>> +		return;
> Probably a overkill here, please check if this will ever hit? 

I have addressed this in next patchset.

> 
>> +
>> +	if (!of_property_read_u32(np, "limit-hs-gear", &hs_gear)) {
>> +		host_params->hs_tx_gear = hs_gear;
>> +		host_params->hs_rx_gear = hs_gear;
>> +	}
>> +
>> +	if (!of_property_read_string(np, "limit-rate", &hs_rate)) {
>> +		if (!strcmp(hs_rate, "rate-a"))
>> +			host_params->hs_rate = PA_HS_MODE_A;
>> +		else if (!strcmp(hs_rate, "rate-b"))
>> +			host_params->hs_rate = PA_HS_MODE_B;
>> +		else
>> +			dev_warn(hba->dev, "Invalid limit-rate: %s\n",
>> hs_rate);
>> +	}
>> +}
>> +EXPORT_SYMBOL_GPL(ufshcd_parse_limits);
>> +
>>  void ufshcd_init_host_params(struct ufs_host_params *host_params)  {
>>  	*host_params = (struct ufs_host_params){ diff --git
>> a/drivers/ufs/host/ufshcd-pltfrm.h b/drivers/ufs/host/ufshcd-pltfrm.h
>> index 3017f8e8f93c..1617f2541273 100644
>> --- a/drivers/ufs/host/ufshcd-pltfrm.h
>> +++ b/drivers/ufs/host/ufshcd-pltfrm.h
>> @@ -29,6 +29,7 @@ int ufshcd_negotiate_pwr_params(const struct
>> ufs_host_params *host_params,
>>  				const struct ufs_pa_layer_attr *dev_max,
>>  				struct ufs_pa_layer_attr *agreed_pwr);  void
>> ufshcd_init_host_params(struct ufs_host_params *host_params);
>> +void ufshcd_parse_limits(struct ufs_hba *hba, struct ufs_host_params
>> +*host_params);
>>  int ufshcd_pltfrm_init(struct platform_device *pdev,
>>  		       const struct ufs_hba_variant_ops *vops);  void
>> ufshcd_pltfrm_remove(struct platform_device *pdev);
>> --
>> 2.50.1
> 
>