[PATCH] usb: dwc3: gadget: ack pending events while waiting for the halt

[Johannes Schneider <johannes.schneider@leica-geosystems.com>]

The controller sets DSTS.DEVCTRLHLT only once every event in the event
buffer has been acknowledged. Linux relies on its interrupt handler
doing that while dwc3_gadget_run_stop() polls; barebox has no
interrupts, and gadget_unbind_driver() unregisters the UDC poller
before it disconnects. Any event left pending at that point keeps the
controller running, and the poll ends in its 2 s timeout with
-ETIMEDOUT.

On an i.MX8MP board with the gadget enumerated by a host, 1 to 15
events (GEVNTCOUNT 4 to 60) were pending on most boots, and each such
boot lost 2.0 s between the start of shutdown_barebox() and the jump
to Linux; with the events acknowledged, the controller halts within
1 ms.

The gadget is being stopped, so acknowledge the events from the poll
loop without processing them, keeping lpos in step with the hardware.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>
---
 drivers/usb/dwc3/gadget.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 8b26a0c102..46a70231a7 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2322,6 +2322,19 @@ static void __dwc3_gadget_set_speed(struct dwc3 *dwc)
 	dwc3_writel(dwc->regs, DWC3_DCFG, reg);
 }
 
+static void dwc3_gadget_discard_events(struct dwc3 *dwc)
+{
+	struct dwc3_event_buffer *evt = dwc->ev_buf;
+	u32 count;
+
+	count = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0)) & DWC3_GEVNTCOUNT_MASK;
+	if (!count)
+		return;
+
+	evt->lpos = (evt->lpos + count) % evt->length;
+	dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), count);
+}
+
 static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
 {
 	u32			reg;
@@ -2356,6 +2369,9 @@ static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
 
 	do {
 		udelay(1000);
+		/* the controller only halts once pending events are acked */
+		if (!is_on)
+			dwc3_gadget_discard_events(dwc);
 		reg = dwc3_readl(dwc->regs, DWC3_DSTS);
 		reg &= DWC3_DSTS_DEVCTRLHLT;
 	} while (--timeout && !(!is_on ^ !reg));

base-commit: 75819f9e196e2da048e96c8589898fdc38ef8e7a
-- 
2.53.0