scsi: 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 <[email protected]>
Signed-off-by: Nitin Rawat <[email protected]>
Signed-off-by: Ram Kumar Dwivedi <[email protected]>
Reviewed-by: Alim Akhtar <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: Ram Kumar Dwivedi

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){

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);