On 24.2.2022 22.21, Alan Stern wrote: > On Thu, Feb 24, 2022 at 09:16:05PM +0100, Heiner Kallweit wrote: >> On 24.02.2022 21:06, Jack Pham wrote: >>> On Wed, Feb 23, 2022 at 05:13:03PM -0500, Alan Stern wrote: >>>> On Wed, Feb 23, 2022 at 09:58:56PM +0100, Heiner Kallweit wrote: >>>>> On 23.02.2022 15:17, Alan Stern wrote: >>>>>> Don't change register_root_hub(). Just change xhci_plat_probe(); make >>>>>> it skip the second call to usb_add_hcd() if there are no USB-3 ports. >>> >>> I believe this had been attempted in the past, but it does not appear >>> that patch was ever accepted: >>> >>> https://lore.kernel.org/linux-usb/1517221474-19627-1-git-send-email-tqnguyen@xxxxxxx/ >>> >> I also found that xhci at several places relies on a proper shared_hcd, >> even if there are no USB3 ports. Therefore maybe go with the less invasive >> original version of my patch? >> >> https://www.spinics.net/lists/linux-usb/msg222998.html > > The patch that Jack refers to, written by Tung Nguyen, does always > create the shared_hcd. It simply avoids registering the shared_hcd > when there are no USB-3 ports. > > You should try that patch and see if it works on your system. > > Alan Stern > >>> Jack >>> >>>>> This works on my system. However a consequence is that xhci->shared_hcd >>>>> is NULL. >>>> >>>> Why is that? xhci->shared_hcd doesn't get set in usb_add_hcd(), so >>>> skipping that call shouldn't cause it to be NULL. >>>> >>>> Note: If you skip calling usb_add_hcd(), you will also have to skip the >>>> corresponding call to usb_remove_hcd(). There may be a few more >>>> subtleties involved as well; like I said before, I'm not an expert on >>>> this driver. You should ask the xhci-hcd maintainer for advice. I think we need to start supporting xHC conreollers with just one roothub. Only call usb_add_hcd() once in those cases. Even prepare for special cases where xHCI only has usb3 ports (usb2 pins routed to a different host controller) Currently driver reads port capabilities in: usb_add_hcd() hcd->driver->reset ...-> xhci_gen_setup() xhci_gen_setup() xhci_init(hcd) xhci_mem_init() xhci_setup_port_arrays() Driver makes some assumptions based on if hcd is primary or not early in xhci_gen_setup(), and initializes values like hcd->speed = HCD_USB2; Should be doable, changes needed in at least xhci_run(), xhci_stop(), xhci_resume(), xhci_suspend(), xhci_gen_setup() and probe. -Mathias
