[PATCH] usb: hub: Per-port setting to reduce TRSTRCY to 10 ms

[Nicolas Boichat]

Currently, the USB hub core waits for 50 ms after enumerating the
device. This was added to help "some high speed devices" to
enumerate (b789696af8 "[PATCH] USB: relax usbcore reset timings").

On some devices, the time-to-active is important, so we provide
a per-port option to reduce the time to what the USB specification
requires: 10 ms.

Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
---

Reduces enumeration time by ~40ms in conjunction with previous
patch/quirk (or ~80ms on its own).

 Documentation/ABI/testing/sysfs-bus-usb | 4 ++++
 drivers/usb/core/hub.c                  | 6 +++++-
 include/linux/usb.h                     | 3 +++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index a31a66d62cbba..08d456e07b538 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -206,6 +206,10 @@ Description:
 		   using /sys/module/usbcore/parameters/old_scheme_first, but
 		   it is often not desirable as the new scheme was introduced to
 		   increase compatibility with more devices.
+		 - Bit 1 reduces TRSTRCY to the 10 ms that are required by the
+		   USB 2.0 specification, instead of the 50 ms that are normally
+		   used to help make enumeration work better on some high speed
+		   devices.
 
 What:		/sys/bus/usb/devices/.../(hub interface)/portX/over_current_count
 Date:		February 2018
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index f900f66a62856..26c2438d28893 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2879,7 +2879,11 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
 done:
 	if (status == 0) {
 		/* TRSTRCY = 10 ms; plus some extra */
-		msleep(10 + 40);
+		if (port_dev->quirks & USB_PORT_QUIRK_FAST_ENUM)
+			usleep_range(10000, 12000);
+		else
+			msleep(10 + 40);
+
 		if (udev) {
 			struct usb_hcd *hcd = bus_to_hcd(udev->bus);
 
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 2ade17992ed66..4cdd515a4385f 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -496,6 +496,9 @@ enum usb_port_connect_type {
 /* For the given port, prefer the old (faster) enumeration scheme. */
 #define USB_PORT_QUIRK_OLD_SCHEME	BIT(0)
 
+/* Decrease TRSTRCY to 10ms during device enumeration. */
+#define USB_PORT_QUIRK_FAST_ENUM	BIT(1)
+
 /*
  * USB 2.0 Link Power Management (LPM) parameters.
  */
-- 
2.17.0.921.gf22659ad46-goog