linux-kernel - [PATCH V6 3/4] ufs: pltfrm: Add DT support to limit HS gear and gear rate

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Message-ID: <20250917140933.2042689-4-quic_rdwivedi@quicinc.com>
Date: Wed, 17 Sep 2025 19:39:32 +0530
From: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
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 V6 3/4] ufs: pltfrm: Add DT support to limit HS gear and gear rate

Introduce parsing of 'limit-hs-gear' and 'limit-gear-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 | 33 ++++++++++++++++++++++++++++++++
 drivers/ufs/host/ufshcd-pltfrm.h |  1 +
 2 files changed, 34 insertions(+)

diff --git a/drivers/ufs/host/ufshcd-pltfrm.c b/drivers/ufs/host/ufshcd-pltfrm.c
index ffe5d1d2b215..c2dafb583cf5 100644
--- a/drivers/ufs/host/ufshcd-pltfrm.c
+++ b/drivers/ufs/host/ufshcd-pltfrm.c
@@ -430,6 +430,39 @@ int ufshcd_negotiate_pwr_params(const struct ufs_host_params *host_params,
 }
 EXPORT_SYMBOL_GPL(ufshcd_negotiate_pwr_params);
 
+/**
+ * ufshcd_parse_gear_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-gear-rate": Specifies the max High-Speed rate.
+ */
+void ufshcd_parse_gear_limits(struct ufs_hba *hba, struct ufs_host_params *host_params)
+{
+	struct device_node *np = hba->dev->of_node;
+	u32 hs_gear;
+	const char *hs_rate;
+
+	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-gear-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 rate: %s\n", hs_rate);
+	}
+}
+EXPORT_SYMBOL_GPL(ufshcd_parse_gear_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..0a18a8aed94d 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_gear_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