thunderbolt: Add support for NHI mailbox

The host controller includes two sets of registers that are used to
communicate with the firmware. Add functions that can be used to access
these registers.

This code is based on the work done by Amir Levy and Michael Jamet.

Signed-off-by: Michael Jamet <michael.jamet@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/thunderbolt/nhi.h b/drivers/thunderbolt/nhi.h
index 8bd9b4e..446ff6d 100644
--- a/drivers/thunderbolt/nhi.h
+++ b/drivers/thunderbolt/nhi.h
@@ -143,6 +143,22 @@ static inline int ring_tx(struct tb_ring *ring, struct ring_frame *frame)
 	return __ring_enqueue(ring, frame);
 }
 
+enum nhi_fw_mode {
+	NHI_FW_SAFE_MODE,
+	NHI_FW_AUTH_MODE,
+	NHI_FW_EP_MODE,
+	NHI_FW_CM_MODE,
+};
+
+enum nhi_mailbox_cmd {
+	NHI_MAILBOX_SAVE_DEVS = 0x05,
+	NHI_MAILBOX_DRV_UNLOADS = 0x07,
+	NHI_MAILBOX_ALLOW_ALL_DEVS = 0x23,
+};
+
+int nhi_mailbox_cmd(struct tb_nhi *nhi, enum nhi_mailbox_cmd cmd, u32 data);
+enum nhi_fw_mode nhi_mailbox_mode(struct tb_nhi *nhi);
+
 /*
  * PCI IDs used in this driver from Win Ridge forward. There is no
  * need for the PCI quirk anymore as we will use ICM also on Apple