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@bootlin.com>
Link: https://lore.kernel.org/r/20250910160730.585303-1-herve.codina@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/dwc2/params.c b/drivers/usb/dwc2/params.c
index ea6bd537e3374306429ed203e2a06af4211774a0..091bfcfef753019f42f3d445455e4e1bab12e9ad 100644 (file)
--- 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;