[PATCH v3 5/6] usb: dwc2: hcd: don't disable/enable external vbus by system suspend/resume

[Fabrice Gasnier]

It's not required to remove port power upon system suspend, as explained
in commit 113f86d0c302 ("usb: dwc2: Update partial power down entering by
system suspend"). It can be addressed with hub ctrl (USB_PORT_FEAT_POWER).

PM suspend flow doesn't disable vbus while in host mode (neither by
clearing HPRT0_PWR nor by calling dwc2_vbus_supply_exit()). In sequence:
- dwc2_port_suspend() - enters clock gating (set lx_state to DWC2_L2)
- _dwc2_hcd_suspend() - nothing more to do as already in L2.

PM resume flow after wakeup (two cases as registers may have been lost)
- _dwc2_hcd_resume() - checks HPRT0_CONNSTS
1 - if set (registers not lost) - nothing more to do.
  - followed by dwc2_port_resume() - exits clock gating (sets lx_state to
    DWC2_L0)
2 - if NOT set - exits clock gating, re-initializes the controller,
    restores HPRT0_PWR and calls dwc2_vbus_supply_init() unbalanced.

For the 2nd case, it's unbalanced / enabled each time it happens: the
vbus regulator enable count constantly increase. As a result, vbus
won't be turned off in case the role changes later to device mode.

So remove the disable/enable of external vbus in bus suspend/resume
routines to avoid this. Moreover, setting/restoring HPRT0_PWR for the
2nd case will simply make the vbus regulator enable count to be aligned
with it.

Fixes: 113f86d0c302 ("usb: dwc2: Update partial power down entering by system suspend")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxxxxxxx>
---
Changes in v3:
- Sashiko comment (state desync leaves VBUS regulator permanently off)
  Add a dwc2_vbus_supply_restore() to check regulator enable state
  during hcd resume, if it has been turned off earlier, enable it,
  so it is kept sync'ed with PWR bit that gets set.

Changes in v2:
- rephrase commit message since Sashiko review. Hopefully it better
  explains the issue, and why HPRT0_PWR is kept synchronized with
  external vbus supply.
---
 drivers/usb/dwc2/hcd.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index cae9d7e13d47..54e3b5698642 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -147,6 +147,20 @@ static int dwc2_vbus_supply_exit(struct dwc2_hsotg *hsotg)
 	return 0;
 }
 
+static int dwc2_vbus_supply_restore(struct dwc2_hsotg *hsotg)
+{
+	int ret;
+
+	if (!hsotg->vbus_supply)
+		return 0;
+
+	ret = regulator_is_enabled(hsotg->vbus_supply);
+	if (!ret)
+		return regulator_enable(hsotg->vbus_supply);
+
+	return ret < 0 ? ret : 0;
+}
+
 /**
  * dwc2_enable_host_interrupts() - Enables the Host mode interrupts
  *
@@ -4388,10 +4402,6 @@ static int _dwc2_hcd_suspend(struct usb_hcd *hcd)
 		goto skip_power_saving;
 	}
 
-	spin_unlock_irqrestore(&hsotg->lock, flags);
-	dwc2_vbus_supply_exit(hsotg);
-	spin_lock_irqsave(&hsotg->lock, flags);
-
 	/* Ask phy to be suspended */
 	if (!IS_ERR_OR_NULL(hsotg->uphy)) {
 		spin_unlock_irqrestore(&hsotg->lock, flags);
@@ -4500,9 +4510,14 @@ static int _dwc2_hcd_resume(struct usb_hcd *hcd)
 		spin_lock_irqsave(&hsotg->lock, flags);
 	}
 
-	/* Enable external vbus supply after resuming the port. */
 	spin_unlock_irqrestore(&hsotg->lock, flags);
-	dwc2_vbus_supply_init(hsotg);
+	/*
+	 * Restore external vbus supply after resuming the port.
+	 * Keeps vbus_supply in sync with HPRT0_PWR set here after.
+	 */
+	ret = dwc2_vbus_supply_restore(hsotg);
+	if (ret)
+		return ret;
 
 	/* Wait for controller to correctly update D+/D- level */
 	usleep_range(3000, 5000);

-- 
2.43.0