usb: dwc2: Skip clock gating on Samsung SoCs

Commit 0112b7ce ("usb: dwc2: Update dwc2_handle_usb_suspend_intr
function.") changed the way the driver handles power down modes in a such
way that it uses clock gating when no other power down mode is available.

This however doesn't work well on the DWC2 implementation used on the
Samsung SoCs. When a clock gating is enabled, system hangs. It looks that
the proper clock gating requires some additional glue code in the shared
USB2 PHY and/or Samsung glue code for the DWC2. To restore driver
operation on the Samsung SoCs simply skip enabling clock gating mode
until one finds what is really needed to make it working reliably.

Fixes: 0112b7ce ("usb: dwc2: Update dwc2_handle_usb_suspend_intr function.")
Cc: stable <stable@vger.kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20210716050127.4406-1-m.szyprowski@samsung.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc2/core.h

@@ -383,6 +383,9 @@ enum dwc2_ep0_state {
  *			0 - No (default)
  *			1 - Partial power down
  *			2 - Hibernation
+ * @no_clock_gating:	Specifies whether to avoid clock gating feature.
+ *			0 - No (use clock gating)
+ *			1 - Yes (avoid it)
  * @lpm:		Enable LPM support.
  *			0 - No
  *			1 - Yes
@@ -480,6 +483,7 @@ struct dwc2_core_params {
 #define DWC2_POWER_DOWN_PARAM_NONE		0
 #define DWC2_POWER_DOWN_PARAM_PARTIAL		1
 #define DWC2_POWER_DOWN_PARAM_HIBERNATION	2
+	bool no_clock_gating;
 
 	bool lpm;
 	bool lpm_clock_gating;

drivers/usb/dwc2/core_intr.c

@@ -556,7 +556,8 @@ static void dwc2_handle_usb_suspend_intr(struct dwc2_hsotg *hsotg)
 				 * If neither hibernation nor partial power down are supported,
 				 * clock gating is used to save power.
 				 */
-				dwc2_gadget_enter_clock_gating(hsotg);
+				if (!hsotg->params.no_clock_gating)
+					dwc2_gadget_enter_clock_gating(hsotg);
 			}
 
 			/*

drivers/usb/dwc2/hcd.c

@@ -3338,7 +3338,8 @@ int dwc2_port_suspend(struct dwc2_hsotg *hsotg, u16 windex)
 		 * If not hibernation nor partial power down are supported,
 		 * clock gating is used to save power.
 		 */
-		dwc2_host_enter_clock_gating(hsotg);
+		if (!hsotg->params.no_clock_gating)
+			dwc2_host_enter_clock_gating(hsotg);
 		break;
 	}
 
@@ -4402,7 +4403,8 @@ static int _dwc2_hcd_suspend(struct usb_hcd *hcd)
 		 * If not hibernation nor partial power down are supported,
 		 * clock gating is used to save power.
 		 */
-		dwc2_host_enter_clock_gating(hsotg);
+		if (!hsotg->params.no_clock_gating)
+			dwc2_host_enter_clock_gating(hsotg);
 
 		/* After entering suspend, hardware is not accessible */
 		clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);

drivers/usb/dwc2/params.c

@@ -76,6 +76,7 @@ static void dwc2_set_s3c6400_params(struct dwc2_hsotg *hsotg)
 	struct dwc2_core_params *p = &hsotg->params;
 
 	p->power_down = DWC2_POWER_DOWN_PARAM_NONE;
+	p->no_clock_gating = true;
 	p->phy_utmi_width = 8;
 }