[PATCH 10/12] usb: core: add power sequence handling for USB devices

Some hard-wired USB devices need to do power sequence to let the
device work normally, the typical power sequence like: enable USB
PHY clock, toggle reset pin, etc. But current Linux USB driver
lacks of such code to do it, it may cause some hard-wired USB devices
works abnormal or can't be recognized by controller at all.

In this patch, it will do power on sequence at hub's probe for all
devices under this hub (includes root hub) if this device is described
at dts and there is a phandle "usb-pwrseq" for it.

At hub_disconnect, it will do power off sequence which is at powered on
list.

Signed-off-by: Peter Chen <redacted>
---
 drivers/usb/core/hub.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++---
 drivers/usb/core/hub.h |  1 +
 include/linux/pwrseq.h |  6 +++++
 3 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index bee1351..cc0f942 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c

@@ -26,6 +26,7 @@
 #include <linux/mutex.h>
 #include <linux/random.h>
 #include <linux/pm_qos.h>
+#include <linux/pwrseq.h>
 
 #include <asm/uaccess.h>
 #include <asm/byteorder.h>

@@ -1684,6 +1685,66 @@ static void hub_release(struct kref *kref)
 
 static unsigned highspeed_hubs;
 
+static void hub_of_pwrseq_off(struct usb_interface *intf)
+{
+	struct usb_hub *hub = usb_get_intfdata(intf);