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authorSarah Sharp <sarah.a.sharp@linux.intel.com>2013-09-30 18:26:28 +0400
committerSarah Sharp <sarah.a.sharp@linux.intel.com>2013-10-16 23:24:19 +0400
commitde68bab4fa96014cfaa6fcbcdb9750e32969fb86 (patch)
treefae95986070b2c2a21366bf8ae568aa224787adb /include/linux/usb.h
parent58e21f73975ec927119370635bf68b9023831c56 (diff)
downloadlinux-de68bab4fa96014cfaa6fcbcdb9750e32969fb86.tar.xz
usb: Don't enable USB 2.0 Link PM by default.
How it's supposed to work: -------------------------- USB 2.0 Link PM is a lower power state that some newer USB 2.0 devices support. USB 3.0 devices certified by the USB-IF are required to support it if they are plugged into a USB 2.0 only port, or a USB 2.0 cable is used. USB 2.0 Link PM requires both a USB device and a host controller that supports USB 2.0 hardware-enabled LPM. USB 2.0 Link PM is designed to be enabled once by software, and the host hardware handles transitions to the L1 state automatically. The premise of USB 2.0 Link PM is to be able to put the device into a lower power link state when the bus is idle or the device NAKs USB IN transfers for a specified amount of time. ...but hardware is broken: -------------------------- It turns out many USB 3.0 devices claim to support USB 2.0 Link PM (by setting the LPM bit in their USB 2.0 BOS descriptor), but they don't actually implement it correctly. This manifests as the USB device refusing to respond to transfers when it is plugged into a USB 2.0 only port under the Haswell-ULT/Lynx Point LP xHCI host. These devices pass the xHCI driver's simple test to enable USB 2.0 Link PM, wait for the port to enter L1, and then bring it back into L0. They only start to break when L1 entry is interleaved with transfers. Some devices then fail to respond to the next control transfer (usually a Set Configuration). This results in devices never enumerating. Other mass storage devices (such as a later model Western Digital My Passport USB 3.0 hard drive) respond fine to going into L1 between control transfers. They ACK the entry, come out of L1 when the host needs to send a control transfer, and respond properly to those control transfers. However, when the first READ10 SCSI command is sent, the device NAKs the data phase while it's reading from the spinning disk. Eventually, the host requests to put the link into L1, and the device ACKs that request. Then it never responds to the data phase of the READ10 command. This results in not being able to read from the drive. Some mass storage devices (like the Corsair Survivor USB 3.0 flash drive) are well behaved. They ACK the entry into L1 during control transfers, and when SCSI commands start coming in, they NAK the requests to go into L1, because they need to be at full power. Not all USB 3.0 devices advertise USB 2.0 link PM support. My Point Grey USB 3.0 webcam advertises itself as a USB 2.1 device, but doesn't have a USB 2.0 BOS descriptor, so we don't enable USB 2.0 Link PM. I suspect that means the device isn't certified. What do we do about it? ----------------------- There's really no good way for the kernel to test these devices. Therefore, the kernel needs to disable USB 2.0 Link PM by default, and distros will have to enable it by writing 1 to the sysfs file /sys/bus/usb/devices/../power/usb2_hardware_lpm. Rip out the xHCI Link PM test, since it's not sufficient to detect these buggy devices, and don't automatically enable LPM after the device is addressed. This patch should be backported to kernels as old as 3.11, that contain the commit a558ccdcc71c7770c5e80c926a31cfe8a3892a09 "usb: xhci: add USB2 Link power management BESL support". Without this fix, some USB 3.0 devices will not enumerate or work properly under USB 2.0 ports on Haswell-ULT systems. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: stable@vger.kernel.org
Diffstat (limited to 'include/linux/usb.h')
-rw-r--r--include/linux/usb.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 055ba74bee80..7454865ad148 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -475,7 +475,8 @@ struct usb3_lpm_parameters {
* @lpm_capable: device supports LPM
* @usb2_hw_lpm_capable: device can perform USB2 hardware LPM
* @usb2_hw_lpm_besl_capable: device can perform USB2 hardware BESL LPM
- * @usb2_hw_lpm_enabled: USB2 hardware LPM enabled
+ * @usb2_hw_lpm_enabled: USB2 hardware LPM is enabled
+ * @usb2_hw_lpm_allowed: Userspace allows USB 2.0 LPM to be enabled
* @usb3_lpm_enabled: USB3 hardware LPM enabled
* @string_langid: language ID for strings
* @product: iProduct string, if present (static)
@@ -548,6 +549,7 @@ struct usb_device {
unsigned usb2_hw_lpm_capable:1;
unsigned usb2_hw_lpm_besl_capable:1;
unsigned usb2_hw_lpm_enabled:1;
+ unsigned usb2_hw_lpm_allowed:1;
unsigned usb3_lpm_enabled:1;
int string_langid;