usb: dwc3: workaround: metastability state on Run/Stop bit

All revisions prior to 2.20a have a known issue which
causes metastability state on Run/Stop bit if we
configure the core to work on any of the USB2-only
speeds.

The suggested workaround is just to never configure the
core to anything other than SuperSpeed.

Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 5255fe975ea1..dda56b8f8617 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1356,7 +1356,24 @@ static int dwc3_gadget_start(struct usb_gadget *g,
 
         reg = dwc3_readl(dwc->regs, DWC3_DCFG);
         reg &= ~(DWC3_DCFG_SPEED_MASK);
-        reg |= dwc->maximum_speed;
+
+        /**
+         * WORKAROUND: DWC3 revision < 2.20a have an issue
+         * which would cause metastability state on Run/Stop
+         * bit if we try to force the IP to USB2-only mode.
+         *
+         * Because of that, we cannot configure the IP to any
+         * speed other than the SuperSpeed
+         *
+         * Refers to:
+         *
+         * STAR#9000525659: Clock Domain Crossing on DCTL in
+         * USB 2.0 Mode
+         */
+        if (dwc->revision < DWC3_REVISION_220A)
+                reg |= DWC3_DCFG_SUPERSPEED;
+        else
+                reg |= dwc->maximum_speed;
         dwc3_writel(dwc->regs, DWC3_DCFG, reg);
 
         dwc->start_config_issued = false;