U-Boot support for IMX8MP dual-role

[Tim Harvey]

Greetings,

I'm wondering if anyone has done any work to get dual-role USB working
for the IMX8MP (or any other dwc3 host based board) and how they went
about it if so.

The imx8mp-venice-gw74xx has dual-role support through a USB Type-C
connector with a TPS25821 (driverless) that monitors the CC signals
and manages VBUS, as well as asserts gpio's:
FAULT# - pinmuxed to OC pin
SINK# - used as GPIO for role
POL# - used for SS mux to connector

For linux this is managed with a usb-role-switch dt prop and a
connector node with compatible of gpio-usb-b-connector and id-gpios
[1]. I did not see anything like that in use in U-Boot for dwc3 hosts
but perhaps I was looking in the wrong place.

For U-Boot I can get this type-C connector to work in host mode only
by changing dr_mode="otg" to dr_mode="host". With the default dt prop
dr_mode=otg dwc3-generic-peripheral is bound instead of
dwc3-generic-host thus no host controller is found.

It seems to me that dwc3_glue_bind needs support added to be able to
check id-gpios or vbus-gpios if usb-role-switch and something like
gpio-usb-b-connector or linux,extcon-usb-gpio are used. Does this
sound like the correct implementation?

I notice that drivers/usb/host/xhci-dwc3.c which is a driver for the
dwc3 core (compatible snps,dwc3) and this does look at usb-role-swich
however this driver as a subnode of fsl,imx8mp-dwc3 (glue) does not
bind and perhaps that is an issue. In that driver usb-role-switch
causes the driver to use role-switch-default-mode for the default mode
which still does not look at an id/vbus pin so that would not be
feature complete either.

Best Regards,

TIm
1 https://git.kernel.org/pub/scm/linux/kernel/git/shawnguo/linux.git/commit/?h=for-next&id=c8a4192d238e9258ab0bc916b3c138a4722af215