Re: [RFC PATCH] USB:XHCI:Modify XHCI driver for USB2.0 controller

Mathias Nyman
2021-02-26T09:24:40Z

On 26.2.2021 10.21, Longfang Liu wrote:
> Our current XHCI hardware controller has been customized to only
> support USB 2.0 ports. When using the current xhci driver, an xhci
> controller device and an ehci controller device will be created
> automatically. We want the driver to create only one ehci controller.
> After modifying the driver as follows, an error will occur.
> Is there any other modification method?

The xhci driver relies on the existence of both a main and a shared hcd.
One hcd for handing USB 2 (and slower) and the other for USB 3 devices.

As one example xhci_run(hcd) needs to be called for both hcds, first call
sets up things, second one calls xhci_start() that makes the controller run.

It's probably possible to modify the driver to support xHCI hosts with only
USB 2 ports, but requires a lot more work.

>
> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
> ---
> drivers/usb/host/xhci-pci.c | 15 ++-------------
> 1 file changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
> index ef513c2..7296aad 100644
> --- a/drivers/usb/host/xhci-pci.c
> +++ b/drivers/usb/host/xhci-pci.c
> @@ -364,26 +364,15 @@ static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
> /* USB 2.0 roothub is stored in the PCI device now. */
> hcd = dev_get_drvdata(&dev->dev);
> xhci = hcd_to_xhci(hcd);
> - xhci->shared_hcd = usb_create_shared_hcd(&xhci_pci_hc_driver, &dev->dev,
> - pci_name(dev), hcd);
> - if (!xhci->shared_hcd) {
> - retval = -ENOMEM;
> - goto dealloc_usb2_hcd;
> - }
> -
> + xhci->shared_hcd = NULL;
> retval = xhci_ext_cap_init(xhci);
> if (retval)
> goto put_usb3_hcd;
>
> - retval = usb_add_hcd(xhci->shared_hcd, dev->irq,
> + retval = usb_add_hcd(xhci->main_hcd, dev->irq,
> IRQF_SHARED);
> if (retval)
> goto put_usb3_hcd;
> - /* Roothub already marked as USB 3.0 speed */
> -
> - if (!(xhci->quirks & XHCI_BROKEN_STREAMS) &&
> - HCC_MAX_PSA(xhci->hcc_params) >= 4)
> - xhci->shared_hcd->can_do_streams = 1;
>
> /* USB-2 and USB-3 roothubs initialized, allow runtime pm suspend */
> pm_runtime_put_noidle(&dev->dev);
>

Something like the above could of course not be accepted upstream. We can't break existing
functionality to support one modified xHCI.

Thanks
Mathias