usb: dwc3: core: do not use 3.0 clock when operating in 2.0 mode

In the 3.0 device core, if the core is programmed to operate in
2.0 only, then setting the GUCTL1.DEV_FORCE_20_CLK_FOR_30_CLK makes
the internal 2.0(utmi/ulpi) clock to be routed as the 3.0 (pipe)
clock. Enabling this feature allows the pipe3 clock to be not-running
when forcibly operating in 2.0 device mode.

Tested-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: Bin Yang <yangbin@rock-chips.com>
Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20220228135700.1089526-6-pgwipeout@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.c

@@ -1167,6 +1167,11 @@ static int dwc3_core_init(struct dwc3 *dwc)
 		if (dwc->parkmode_disable_ss_quirk)
 			reg |= DWC3_GUCTL1_PARKMODE_DISABLE_SS;
 
+		if (DWC3_VER_IS_WITHIN(DWC3, 290A, ANY) &&
+		    (dwc->maximum_speed == USB_SPEED_HIGH ||
+		     dwc->maximum_speed == USB_SPEED_FULL))
+			reg |= DWC3_GUCTL1_DEV_FORCE_20_CLK_FOR_30_CLK;
+
 		dwc3_writel(dwc->regs, DWC3_GUCTL1, reg);
 	}
 

drivers/usb/dwc3/core.h

@@ -259,6 +259,7 @@
 /* Global User Control 1 Register */
 #define DWC3_GUCTL1_DEV_DECOUPLE_L1L2_EVT	BIT(31)
 #define DWC3_GUCTL1_TX_IPGAP_LINECHECK_DIS	BIT(28)
+#define DWC3_GUCTL1_DEV_FORCE_20_CLK_FOR_30_CLK	BIT(26)
 #define DWC3_GUCTL1_DEV_L1_EXIT_BY_HW		BIT(24)
 #define DWC3_GUCTL1_PARKMODE_DISABLE_SS		BIT(17)