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

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Message-ID: <3a9001dc1c8b$2d303c40$8790b4c0$@samsung.com>
Date: Wed, 3 Sep 2025 09:58:16 +0530
From: "Alim Akhtar" <alim.akhtar@...sung.com>
To: "'Ram Kumar Dwivedi'" <quic_rdwivedi@...cinc.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



> -----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.

> +*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? 

> +
> +	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