imx8mp USB OTG/dual-role

* imx8mp USB OTG/dual-role
@ 2022-08-30 17:53 ` Tim Harvey
  0 siblings, 0 replies; 14+ messages in thread
From: Tim Harvey @ 2022-08-30 17:53 UTC (permalink / raw)
  To: linux-usb, Linux ARM Mailing List
  Cc: Alexander Stein, Li Jun, Rikard Falkeborn, Lucas Stach,
	Philippe Schenker, Felipe Balbi, Fabio Estevam, Marcel Ziswiler,
	Shawn Guo, Marek Vasut, Francesco Dolcini, Jacky Bai,
	Dong Aisheng, Sascha Hauer, NXP Linux Team,
	Pengutronix Kernel Team

Greetings,

I have an imx8mp board (imx8mp-venice-gw74xx) which has a DWC3 USB
host controller using imx8mp PHY
(drivers/phy/freescale/phy-fsl-imx8mq-usb.c fsl,imx8mp-usb-phy) and
DWC3 host controller core (drivers/usb/dwc3/core.c snps,dwc3) with
imx8mp glue (drivers/usb/dwc3/dwc3-imx8mp.c fsl,imx8mp-dwc3).

One of the 2x USB 3.0 hosts is connected to a USB Type C connector
using a TPS25821 USB power switch and config controller which handles
the CC pins on and VBUS enable as well as drives the mux sel pin of a
USB3 mux to route the USB SS pairs to the appropriate half of the Type
C connector. This device has no I2C or other management bus - only
VBUS, FAULT#, SINK#, and POL# outputs based on CC pins.

I'm not clear how to describe this in the device-tree in order for it
to function as a dual-role controller for host vs device mode.

The TPS25821 has a FAULT# signal that routes to IMX8MP GPIO1_IO13
pinmuxed as MX8MP_IOMUXC_GPIO1_IO13__USB1_OTG_OC and a SINK# signal
that routes to IMX8MP GPIO1_IO10 pinmuxed as
MX8MP_IOMUXC_GPIO1_IO10__USB1_OTG_ID. Additionally the VBUS output of
the TPS25821 also connected to the TypeC VBUS pin routes to the IMX8MP
USB1_VBUS pin.

I've noticed there are currently only 2 other IMX8MP boards in Linux
mainline that specify dr_mode="otg"; the DH electronics i.MX8M Plus
DHCOM SOM (imx8mp-dhcom-som.dtsi), and the Toradex i.MX8M Plus Verdin
SOM (imx8mp-verdin.dtsi). I'm not clear how these are hooked up or if
USB dual-role work on these currently. I did notice that
imx8mp-verdin.dtsi looks like it does not enable the phy or core via
status prop and uses invalid 'over-current-active-low' and
'disable-over-current' dt props.

I am currently using the following with imx8mp-venice-gw74xx:

/* USB1 - Type C front panel */
&usb3_phy0 {
        status = "okay";
};

/* USB1 dwc3 glue */
&usb3_0 {
        fsl,over-current-active-low;
        status = "okay";
};

/* USB1 dwc3 core */
&usb_dwc3_0 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_usb1>;
        dr_mode = "otg";
};

&iomuxc {
        pinctrl_usb1: usb1grp {
                fsl,pins = <
                        MX8MP_IOMUXC_GPIO1_IO13__USB1_OTG_OC    0x140
                        MX8MP_IOMUXC_GPIO1_IO10__USB1_OTG_ID    0x140
                >;
        };
};

And currently v6.0-rc2 enumerates the host controller even without a
Type-C to host cable attached which tells me that OTG_ID isn't doing
its job. I vaguely recall some confusing statements on the IMX
community forum that these pins might not even be used on the IMX8MP.

How should I be describing the device-tree for this scenario in order
to get dual-role behavior?

Best Regards,

Tim

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