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SubjectRe: USB disk speed regression WD Elements - with bisect result 22547c4cc4fe20698a6a85a55b8788859134b8e4
Dne 27.7.2017 v 03:03 Alan Stern napsal(a):
> [Added linux-usb mailing list to CC:]
> Short description of bug: In 4.12 or later, when Zdenek's Western
> Digital disk is attached to an EHCI controller, it ends up connecting
> at full speed to the companion UHCI controller instead. But when
> commit 22547c4cc4fe ("usb: hub: Wait for connection to be reestablished
> after port reset") is reverted, the disk connects correctly at high
> speed.
> On Wed, 26 Jul 2017, Zdenek Kabelac wrote:
>> Dne 25.7.2017 v 21:50 Alan Stern napsal(a):
>>> On Tue, 25 Jul 2017, Zdenek Kabelac wrote:
>>> 08:18 usb 2-2: USB disconnect, device number 2
>>> 08:25 usb 2-2: new high-speed USB device number 3 using ehci-pci
>>> 08:26 usb 2-2: new high-speed USB device number 4 using ehci-pci
>>> If the drive were working entirely correctly, it wouldn't do that.
>>> We could continue futzing around with hardware and driver tests for a
>>> long time. But there may be a shortcut: If you have a USB hub, you
>>> could try attaching the drive through it. It's entirely possible that
>>> this will fix the problem.
>>> If not, you'll have to start doing some very detailed tests. As a
>>> start, you can enable debugging for the usbcore and ehci_hcd drivers
>>> immediately before the test:
>>> echo 'module usbcore =p' >/sys/kernel/debug/dynamic_debug/control
>>> echo 'module ehci_hcd =p' >/sys/kernel/debug/dynamic_debug/control
>>> dmesg -C
>>> Then after the test, see what shows up in the dmesg output. And again,
>>> we'll want to do a comparison. In fact, 4.12 with and without the
>>> commit you identified would make a better comparison than 4.12 vs. 4.8.
>> Hi
>> So here we go with traces - made with freshly compiled recent 4.13-rc2.
>> OK trace is with revert patch applied.
>> BAD trace is the one with it (essentially vaniala master).
>> Trace also has KOBJECT debugging enabled - I think difference is
>> nicely visible between them - but I've no explanation for it.
>> Both traces start with cable detach followed with attachment.
> Okay, I figured out the cause.
> The USB stack assumes that if a high-speed device initialization fails
> and the device is still connected, it means that the device can't run
> properly at high speed and the computer needs to try again at full
> speed. See commit 90da096ee46b ("USB: force handover port to companion
> when hub_port_connect_change fails").
> In Zdenek's case, the device really does disconnect itself before the
> second port reset. If 22547c4cc4fe is present, it causes an extra
> delay -- some 200 ms -- long enough for the device to reconnect again.
> So we appear to be in the situation described above, and the connection
> is switched over to the companion controller.
> If 22547c4cc4fe is not present, the kernel sees that the device is not
> connected at the end of the second reset and gives up trying to
> initialize the device. When the device reconnects about 140 ms later,
> the kernel treats it as a new connection and successfully negotiates a
> high-speed link.
> Zdenek, you check this explanation by commenting out these last two
> lines at the end of hub_port_connect() in drivers/usb/core/hub.c:
> if (hcd->driver->relinquish_port && !hub->hdev->parent)
> hcd->driver->relinquish_port(hcd, port1);
> That should prevent the connection from being handed over to the UHCI
> companion, allowing the device to operate at high speed.


Yep - seems this helped - I've dropped revert and commented those 2 lines
and I've used the very same kernel - and speed was all good:

usb 2-2: new high-speed USB device number 2 using ehci-pci
usb 2-2: new high-speed USB device number 3 using ehci-pci
usb 2-2: New USB device found, idVendor=1058, idProduct=10a8
usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3

So while I'm not sure if this is final fix for USB - this solution surely
solved my WD Element disk attachment issue.



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