The Intel cherrytrail xhci controller has an extended cap mmio-range
which contains registers to control the muxing to the xhci (host mode)
or the dwc3 (device mode) and vbus-detection for the otg usb-phy.
Having a mux driver included in the xhci code (or under drivers/usb/host)
is not desirable. So this commit adds a simple handler for this extended
capability, which creates a platform device with the caps mmio region as
resource, this allows us to write a separate platform mux driver for the
mux.
Note this commit adds a call to the new xhci_ext_cap_init() function
to xhci_pci_probe(), it is added here because xhci_ext_cap_init() must
be called only once. If in the future we also want to handle ext-caps
on non pci XHCI HCDs from xhci_ext_cap_init() a call to it should also
be added to other bus probe paths.
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
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Changes in v2:
-Check xHCI controller PCI device-id instead of only checking for the
Intel Extended capability ID, as the Extended capability ID is used on
other model Intel xHCI controllers too
Changes in v3:
-Add a new generic xhci_ext_cap_init() function and handle the new
XHCI_INTEL_CHT_USB_MUX quirk there.
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