linux-kernel - [PATCH] usb: dwc2: Add support for 'maximum-speed' property

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Message-ID: <20250910160730.585303-1-herve.codina@bootlin.com>
Date: Wed, 10 Sep 2025 18:07:30 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Minas Harutyunyan <hminas@...opsys.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Herve Codina <herve.codina@...tlin.com>
Subject: [PATCH] usb: dwc2: Add support for 'maximum-speed' property

The DWC2 IP can be properly integrated in a SoC to work at high-speed
USB speed but some board issues, EMC constraints or any other reasons
can lead to the need to limit this USB speed at board level.

The device-tree 'maximum-speed' property already exists for this purpose
but is not handled by the DWC2 driver.

Fill this lack adding support for 'maximum-speed' property and so allow
to limit the USB speed in device-tree (board description).

Signed-off-by: Herve Codina <herve.codina@...tlin.com>
---
 drivers/usb/dwc2/params.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/usb/dwc2/params.c b/drivers/usb/dwc2/params.c
index ea6bd537e337..091bfcfef753 100644
--- a/drivers/usb/dwc2/params.c
+++ b/drivers/usb/dwc2/params.c
@@ -1029,11 +1029,33 @@ int dwc2_get_hwparams(struct dwc2_hsotg *hsotg)
 	return 0;
 }
 
+static int dwc2_limit_speed(struct dwc2_hsotg *hsotg)
+{
+	enum usb_device_speed usb_speed;
+
+	usb_speed = usb_get_maximum_speed(hsotg->dev);
+	switch (usb_speed) {
+	case USB_SPEED_LOW:
+		dev_err(hsotg->dev, "Maximum speed cannot be forced to low-speed\n");
+		return -EINVAL;
+	case USB_SPEED_FULL:
+		if (hsotg->params.speed == DWC2_SPEED_PARAM_LOW)
+			break;
+		hsotg->params.speed = DWC2_SPEED_PARAM_FULL;
+		break;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
 typedef void (*set_params_cb)(struct dwc2_hsotg *data);
 
 int dwc2_init_params(struct dwc2_hsotg *hsotg)
 {
 	set_params_cb set_params;
+	int ret;
 
 	dwc2_set_default_params(hsotg);
 	dwc2_get_device_properties(hsotg);
@@ -1051,6 +1073,10 @@ int dwc2_init_params(struct dwc2_hsotg *hsotg)
 		}
 	}
 
+	ret = dwc2_limit_speed(hsotg);
+	if (ret)
+		return ret;
+
 	dwc2_check_params(hsotg);
 
 	return 0;
-- 
2.51.0