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

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Date:   Fri, 28 Sep 2018 19:27:52 +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>,
        <ravisadineni@...omium.org>, <joe@...ches.com>
CC:     <prime.zeng@...ilicon.com>, Jonathan Corbet <corbet@....net>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        "Thymo van Beers" <thymovanbeers@...il.com>,
        Jiri Kosina <jkosina@...e.cz>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>
Subject: [PATCH] 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>
Acked-by: Alan Stern <stern@...land.harvard.edu>
Reviewed-by: Roger Quadros <rogerq@...com>
---
 Documentation/admin-guide/kernel-parameters.txt | 3 ++-
 drivers/usb/core/hub.c                          | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 92eb1f4..151c527 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4610,7 +4610,8 @@
 
 	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 462ce49..fb4e6bb 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2660,11 +2660,13 @@ 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