linux-kernel - [PATCH v2] usb: hub: try old enumeration scheme first for high speed devices

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Date:   Fri, 17 Aug 2018 18:51:52 +0800
From:   Zeng Tao <prime.zeng@...ilicon.com>
To:     <gregkh@...uxfoundation.org>, <stern@...land.harvard.edu>,
        <mathias.nyman@...ux.intel.com>, <drinkcat@...omium.org>,
        <felipe.balbi@...ux.intel.com>, <drake@...lessm.com>,
        <mike.looijmans@...ic.nl>, <joe@...ches.com>
CC:     Zeng Tao <prime.zeng@...ilicon.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        "Thymo van Beers" <thymovanbeers@...il.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        "David Rientjes" <rientjes@...gle.com>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>
Subject: [PATCH v2] usb: hub: try old enumeration scheme first for high speed devices

The new scheme is required just to support legacy low and full-speed
devices. For high speed devices, it will slower the enumeration speed.
So in this patch we try the "old" enumeration scheme first for high speed
devices, and this is what Windows does since Windows 8.

Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
---
Changes in v2:
1. As suggested by Alan, mention in the commit log that this change is
follow what the Window does.
2. As suggested by Roger, update the kernel-parameter description.
---
 Documentation/admin-guide/kernel-parameters.txt | 3 ++-
 drivers/usb/core/hub.c                          | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 533ff5c..95db23c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4453,7 +4453,8 @@
 
 	usbcore.old_scheme_first=
 			[USB] Start with the old device initialization
-			scheme (default 0 = off).
+			scheme,  applies only to low and full-speed devices
+			 (default 0 = off).
 
 	usbcore.usbfs_memory_mb=
 			[USB] Memory limit (in MB) for buffers allocated by
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 1fb2668..d265b19 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2661,10 +2661,13 @@ static bool use_new_scheme(struct usb_device *udev, int retry,
 	int old_scheme_first_port =
 		port_dev->quirks & USB_PORT_QUIRK_OLD_SCHEME;
 
+	int quick_enumeration = (udev->speed == USB_SPEED_HIGH);
+
 	if (udev->speed >= USB_SPEED_SUPER)
 		return false;
 
-	return USE_NEW_SCHEME(retry, old_scheme_first_port || old_scheme_first);
+	return USE_NEW_SCHEME(retry, old_scheme_first_port || old_scheme_first
+			      || quick_enumeration);
 }
 
 /* Is a USB 3.0 port in the Inactive or Compliance Mode state?
-- 
2.7.4