Re: `quirk_usb_handoff_xhci` takes 60 ms with ASM1042

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Greg,


Thank you for the quick reply.

Am 05.05.21 um 10:11 schrieb Greg Kroah-Hartman:
> On Wed, May 05, 2021 at 09:57:44AM +0200, Paul Menzel wrote:

>> On an Asus F2A85-M PRO, BIOS 6601 11/25/2014, with an ASM1042 SuperSpeed USB
>> Host Controller [1b21:1042], and the xHCI drivers built as modules
>>
>>      CONFIG_USB_XHCI_PCI=m
>>      CONFIG_USB_XHCI_HCD=m
>>
>> `quirk_usb_handoff_xhci` takes 60 ms, which is 15 % of the time to reaching
>> `run_init_process()`. I addded some prints, showing the f
>>
>>      [    0.308841] pci 0000:03:00.0: PCI->APIC IRQ transform: INT A -> IRQ 17
>>      [    0.369858] pci 0000:03:00.0: handshake done with timeout = 0
>>      [    0.369862] pci 0000:03:00.0: hc_init reached
>>      [    0.369865] pci 0000:03:00.0: second handshake done
>>      [    0.369869] pci 0000:03:00.0: third handshake done
>>      [    0.369909] pci 0000:03:00.0: quirk_usb_early_handoff+0x0/0x670 took 59661 usecs
>>      […]
>>      [    0.415223] Run /lib/systemd/systemd as init process
>>
>> Is there a way to optimize this, or move it out “the hot path”?
> 
> That's the hardware taking so long, all that function does is make some
> PCI calls to the device.

In your experience, do most devices take that long?

> If the driver is built as a module, there should not be any "hot
> path" here as the module is loaded async when the device is
> discovered, right?
     obj-$(CONFIG_USB_PCI)   += pci-quirks.o

So all quirks are run independently of the USB “variant” (UHCI, OHCI, 
EHCI, xHCI).

Indeed, this driver is built into the Linux kernel.

     $ grep USB_PCI .config
     CONFIG_USB_PCI=y

So, should `pci-quirks.c` be split up to have more fine grained control?

> What is waiting for this module to load in order to cause your init to
> stall?  Perhaps fix your initramfs logic or build the driver into the
> kernel itself to take it off of this "load all the modules and wait"
> path?

Sorry, for causing some confusion. But as written above, this all 
happens before the initrd is involved.


Kind regards,

Paul