Re: USB bus numbering

On Wed, 28 Feb 2007, Jon Smirl wrote:

> On 2/28/07, Alan Stern <[email protected]> wrote:
> > I can't tell just from the end results.  Post the dmesg log showing what
> > happened during boot-up and we'll see.

Skipping irrelevant parts of the log...

> io scheduler noop registered
> io scheduler anticipatory registered
> io scheduler deadline registered
> io scheduler cfq registered (default)

On my system, which is similar to yours, this is where the UHCI and EHCI
controllers are detected.  The driver modules are loaded later.

...
> usbcore: registered new interface driver usbfs
> usbcore: registered new interface driver hub
> usbcore: registered new device driver usb

Apparently ehci-hcd gets loaded somewhere in here.  It doesn't print
a banner line, so we can't be sure.

> USB Universal Host Controller Interface driver v3.0

That's the banner line for uhci-hcd.

> ACPI: PCI Interrupt 0000:00:1d.7[D] -> GSI 23 (level, low) -> IRQ 18
> PCI: Setting latency timer of device 0000:00:1d.7 to 64
> ehci_hcd 0000:00:1d.7: EHCI Host Controller
> ehci_hcd 0000:00:1d.7: new USB bus registered, assigned bus number 1
> ehci_hcd 0000:00:1d.7: debug port 1
> PCI: cache line size of 128 is not supported by device 0000:00:1d.7
> ehci_hcd 0000:00:1d.7: irq 18, io mem 0xffa80800
> ehci_hcd 0000:00:1d.7: USB 2.0 started, EHCI 1.00, driver 10 Dec 2004
> usb usb1: configuration #1 chosen from 1 choice
> hub 1-0:1.0: USB hub found
> hub 1-0:1.0: 8 ports detected

The EHCI controller was probed before any of the UHCI controllers.  Hence
the loading of the two drivers must have occurred in parallel; if the
loading had been serialized then the EHCI probing couldn't have come
between the uhci-hcd banner line and the UHCI probing.

Next the UHCI controllers get probed.

> ACPI: PCI Interrupt 0000:00:1d.0[A] -> GSI 16 (level, low) -> IRQ 19
> PCI: Setting latency timer of device 0000:00:1d.0 to 64
> uhci_hcd 0000:00:1d.0: UHCI Host Controller
> uhci_hcd 0000:00:1d.0: new USB bus registered, assigned bus number 2
> uhci_hcd 0000:00:1d.0: irq 19, io base 0x0000ff80
> usb usb2: configuration #1 chosen from 1 choice
> hub 2-0:1.0: USB hub found
> hub 2-0:1.0: 2 ports detected
> ACPI: PCI Interrupt 0000:00:1d.1[B] -> GSI 19 (level, low) -> IRQ 17
> PCI: Setting latency timer of device 0000:00:1d.1 to 64
> uhci_hcd 0000:00:1d.1: UHCI Host Controller
> uhci_hcd 0000:00:1d.1: new USB bus registered, assigned bus number 3
> uhci_hcd 0000:00:1d.1: irq 17, io base 0x0000ff60
> usb usb3: configuration #1 chosen from 1 choice
> hub 3-0:1.0: USB hub found
> hub 3-0:1.0: 2 ports detected
> ACPI: PCI Interrupt 0000:00:1d.2[C] -> GSI 18 (level, low) -> IRQ 16
> PCI: Setting latency timer of device 0000:00:1d.2 to 64
> uhci_hcd 0000:00:1d.2: UHCI Host Controller
> uhci_hcd 0000:00:1d.2: new USB bus registered, assigned bus number 4
> uhci_hcd 0000:00:1d.2: irq 16, io base 0x0000ff40
> usb usb4: configuration #1 chosen from 1 choice
> hub 4-0:1.0: USB hub found
> hub 4-0:1.0: 2 ports detected
> usb 1-1: new high speed USB device using ehci_hcd and address 2
> ACPI: PCI Interrupt 0000:00:1d.3[A] -> GSI 16 (level, low) -> IRQ 19
> PCI: Setting latency timer of device 0000:00:1d.3 to 64
> uhci_hcd 0000:00:1d.3: UHCI Host Controller
> uhci_hcd 0000:00:1d.3: new USB bus registered, assigned bus number 5
> uhci_hcd 0000:00:1d.3: irq 19, io base 0x0000ff20
> usb usb5: configuration #1 chosen from 1 choice
> hub 5-0:1.0: USB hub found
> hub 5-0:1.0: 2 ports detected

Hyperthreading might be related to your race, but I don't think it is a
necessary ingredient.  Most likely, the hotplug system just starts up two
modprobe processes that run in parallel.

Alan Stern


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