usb: dwc3: implement runtime PM

this patch implements the most basic pm_runtime
support for dwc3. Whenever USB cable is dettached,
then we will allow core to runtime_suspend.

Runtime suspending will involve completely tearing
down event buffers and require a full soft-reset of
the IP.

Note that a further optimization could be
implemented once we decide to support hibernation,
which is to allow runtime_suspend with cable
connected when bus is in U3. That's subject to a
separate patch, however.

Tested-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index 5148c56..94b9fd2 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -763,6 +763,7 @@
  * @lpm_nyet_threshold: LPM NYET response threshold
  * @hird_threshold: HIRD threshold
  * @hsphy_interface: "utmi" or "ulpi"
+ * @connected: true when we're connected to a host, false otherwise
  * @delayed_status: true when gadget driver asks for delayed status
  * @ep0_bounced: true when we used bounce buffer
  * @ep0_expect_in: true when we expect a DATA IN transfer
@@ -773,6 +774,7 @@
  * 	0	- utmi_sleep_n
  * 	1	- utmi_l1_suspend_n
  * @is_fpga: true when we are using the FPGA board
+ * @pending_events: true when we have pending IRQs to be handled
  * @pullups_connected: true when Run/Stop bit is set
  * @setup_packet_pending: true when there's a Setup Packet in FIFO. Workaround
  * @start_config_issued: true when StartConfig command has been issued
@@ -907,6 +909,7 @@
 
 	const char		*hsphy_interface;
 
+	unsigned		connected:1;
 	unsigned		delayed_status:1;
 	unsigned		ep0_bounced:1;
 	unsigned		ep0_expect_in:1;
@@ -914,6 +917,7 @@
 	unsigned		has_lpm_erratum:1;
 	unsigned		is_utmi_l1_suspend:1;
 	unsigned		is_fpga:1;
+	unsigned		pending_events:1;
 	unsigned		pullups_connected:1;
 	unsigned		setup_packet_pending:1;
 	unsigned		three_stage_setup:1;
@@ -1139,6 +1143,7 @@
 #if !IS_ENABLED(CONFIG_USB_DWC3_HOST)
 int dwc3_gadget_suspend(struct dwc3 *dwc);
 int dwc3_gadget_resume(struct dwc3 *dwc);
+void dwc3_gadget_process_pending_events(struct dwc3 *dwc);
 #else
 static inline int dwc3_gadget_suspend(struct dwc3 *dwc)
 {
@@ -1149,6 +1154,10 @@
 {
 	return 0;
 }
+
+static inline void dwc3_gadget_process_pending_events(struct dwc3 *dwc)
+{
+}
 #endif /* !IS_ENABLED(CONFIG_USB_DWC3_HOST) */
 
 #if IS_ENABLED(CONFIG_USB_DWC3_ULPI)