On 21.8.2023 12.55, Hardik Gajjar wrote:
On Fri, Aug 18, 2023 at 04:18:30PM +0300, Mathias Nyman wrote:
On 18.8.2023 12.23, Hardik Gajjar wrote:
xHCI driver starts the response timer after sending each
command to the device. The default value of this timer is
5 seconds (XHCI_CMD_DEFAULT_TIMEOUT = HZ*5). This seems
too high in time crtical use case.
This patch provides an API to change the default value of
the timer from the vendor USB driver.
The default value will be XHCI_CMD_DEFAULT_TIMEOUT (5 sec)
Use case:
According to the Smartphone integration certification
requirement in the automotive, the phone connected via USB
should complete enumeration and user space handshake
within 3 sec.
The above incorrectly makes it sound as if the command timeout
timer causes the delay.
Thank you, Mathias, for your prompt response. I will enhance the message
to provide more specificity in the subsequent patch.
Reducing the response waiting time by setting the smaller
command timer delay helps to speed up overall re-enumeration
process of the USB device in case of device is not responding
properly in first enumeration iteration.
So is this a case where addressing a usb device behind xHC always
fail on the first attempt, i.e. address device command in xhci
never completes. Solution proposed here is to fail faster and
retry?
Is the rootcause known why first enumeration fails?
Does setting old_scheme_first module parameter help?
Yes, you are correct. The problem occurs when setting the address,
and in such cases, this patch helps to fail faster and retry.
Unfortunately, the root cause is unknown. This problem is mainly
observed with Android phones. Upon analyzing the USB analyzer logs,
it seems that the device is not responding to the SET_ADDRESS request.
Is this only seen when connecting the device to a Linux xHCI host at USB 3 speeds?
How about connecting to a windows machine? or USB 2 Linux machine with a EHCI host?
I tried using "old_scheme_first=Y," but that did not help. Below are
the short logs of the first iteration enumeration failure.
The xhci command timeout is more of a xhci internal thing, not sure it's a good
idea to add this to hcd.
Would it make sense to add a timeout parameter to hcd->driver->address_device(hcd, udev)
instead?
First priority should of course be finding out why the first enumeration fails,
and solve that.
Thanks
Mathias
Thanks for the suggestion to modify hcd->driver->address_device.
I will definitely implement it.However to confirm.
So, if I understand correctly, the idea is to avoid exposing any
API from the xhci driver, but instead, create an interface in hcd.c (such as sysfs or API)
and incorporate the delay in address_device as an additional parameter.
On second thought it only makes sense to do this if we can identify the device in advance
and make a quirk for it. But at this stage we don't know anything about the device.
So I guess this depends on the width of the problem.
If this works on windows then we need to figure out what we do differently.
If this fails with all hosts (well xHCI and EHCI) then hcd level change is probably needed.
For xhci we would pass timeout parameter when calling address_device, for other hosts
the timeout for the SET_ADDRESS control transfer would be adjusted.
If this only fails when connected behind a xHCI host then a local xHCI change should do.
However, in that case, modifying xhci is still necessary as the timer is controlled from there.
Yes, xhci changes will be needed.
I suggest adding a timeout parameter to struct xhci_command, and use that when calling
xhci_mod_cmd_timer(). This way we can tailor different timeouts for different commands.
-Mathias
