[RFC PATCH 3/3] usb: dwc3: Issue core soft reset before enabling run/stop

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

It is recommended by the Synopsis databook to issue a DCTL.CSftReset
when reconnecting from a device-initiated disconnect routine.  This
resolves issues with enumeration during fast composition switching
cases, which result in an unknown device on the host.

Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
 drivers/usb/dwc3/core.c   |  4 +---
 drivers/usb/dwc3/core.h   |  2 ++
 drivers/usb/dwc3/gadget.c | 11 +++++++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index f4c09951b517..d128c7f22b01 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -115,8 +115,6 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode)
 	dwc->current_dr_role = mode;
 }
 
-static int dwc3_core_soft_reset(struct dwc3 *dwc);
-
 static void __dwc3_set_mode(struct work_struct *work)
 {
 	struct dwc3 *dwc = work_to_dwc(work);
@@ -261,7 +259,7 @@ u32 dwc3_core_fifo_space(struct dwc3_ep *dep, u8 type)
  * dwc3_core_soft_reset - Issues core soft reset and PHY reset
  * @dwc: pointer to our context structure
  */
-static int dwc3_core_soft_reset(struct dwc3 *dwc)
+int dwc3_core_soft_reset(struct dwc3 *dwc)
 {
 	u32		reg;
 	int		retries = 1000;
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index d418ed55a566..e15b83a6f094 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -1527,6 +1527,8 @@ bool dwc3_has_imod(struct dwc3 *dwc);
 int dwc3_event_buffers_setup(struct dwc3 *dwc);
 void dwc3_event_buffers_cleanup(struct dwc3 *dwc);
 
+int dwc3_core_soft_reset(struct dwc3 *dwc);
+
 #if IS_ENABLED(CONFIG_USB_DWC3_HOST) || IS_ENABLED(CONFIG_USB_DWC3_DUAL_ROLE)
 int dwc3_host_init(struct dwc3 *dwc);
 void dwc3_host_exit(struct dwc3 *dwc);
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 1efa30907d42..94cfbe32da8d 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2572,6 +2572,17 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
 						dwc->ev_buf->length;
 		}
 	} else {
+		/*
+		 * In the Synopsis DesignWare Cores USB3 Databook Rev. 1.90a
+		 * Section 4.1.9, it specifies that for a reconnect after a
+		 * device-initiated disconnect requires a core soft reset
+		 * (DCTL.CSftRst) before enabling the run/stop bit.
+		 */
+		spin_unlock_irqrestore(&dwc->lock, flags);
+		dwc3_core_soft_reset(dwc);
+		spin_lock_irqsave(&dwc->lock, flags);
+
+		dwc3_event_buffers_setup(dwc);
 		__dwc3_gadget_start(dwc);
 	}