Use USB OTG in host mode

[frm]

Hi,
Can I change the configuration of the microUSB OTG in my OLinuxino A64 to use it in "host mode" instead of "pheripheral mode" ?

I only found this post https://www.olimex.com/forum/index.php?topic=4990.0 which mentions a FEX file somewhere... and it's dated 2016

Thanks

[LubOlimex]

Hardware-wise it is possible since there is USB0-ID wire/signal. So the port supports both device and host mode, it is real OTG.

Software-wise I don't think the Olimage image supports it, so some changes to the image are required.

The info you found applies to older sunxi-based images, that used fex files, it does not apply to the Olimage Linux which uses mainline. You'd have to edit dts/dtb. Refer to the Olimage guide, there is info on how to change dts/dtb or kernel:

https://raw.githubusercontent.com/OLIMEX/OLINUXINO/master/DOCUMENTS/OLIMAGE/Olimage-guide.pdf

[frm]

Software-wise I don't think the Olimage image supports it, so some changes to the image are required.

This is really a pity. Right now I don't want to go through the lengthy process of rebuilding the kernel and the image myself, so I'll just use a basic USB hub to expand the single USB host port. It makes the whole setup much less compact thought :-(

Thanks

[winfried]

Since also need this for my A64 Rev.E , to connect a keyboard on the mini USB-OTG, USB-A already used by another device:

You'd have to edit dts/dtb. Refer to the Olimage guide, there is info on how to change dts/dtb or kernel:

Installed the crosscompiler and can make dtb. So what I have to edit ?

found in arch/arm64/boot/dts/allwinner/sun50i-a64-olinuxino-1G.dts

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&usb_otg {
        dr_mode = "otg";
        status = "okay";
};

I cannot figure out what to change, or what mode to define and where to find the documentation for this.

Any hint ?

mfg winfried

[winfried]

First report:

- Measured that the USB-OTG Pin is set to GND with OTG cable and made the mouse test. So the OTG functionality seems to be broken.

Changed the devicetree:

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&usb_otg {
        dr_mode = "host"; /* set to host from otg */
        status = "okay";
};

Result:
3 seconds after boot mouse is detected and is powered  and after 33 second usb0-vbus is disabled and mouse is disconnected. So there is somewhere a timeout or the like.

Suspected the autosuspend, disabling, but still something in the system switches of the usb0-vbus, so disabled "USB Autosuspend" in Linux (Runtime Power Management).

in /boot/uEnv.txt put the line

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optargs=usbcore.autosuspend=-1but this did not help.

What also is suspect is that there is a

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/sys/devices/platform/usb1-vbusbut no

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/sys/devices/platform/usb0-vbus
So I stop for today, any hint is welcome

[LubOlimex]

The problem is the powering. I used AI to analyze what can be done and got it working if I force it in host mode but that is dangerous (in case you want device mode at some point). I will see if I can get it working properly in dual mode and will give you some instructions.

[winfried]

Thanks, will wait for your result.

Just for info:
Also tried to disable the <&reg_drivevbus> for the _vbus-supply ind dts, but didnt help.

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&usbphy {
status = "okay";
usb0_id_det-gpios = <&pio 7 9 GPIO_ACTIVE_HIGH>; /* PH9 */
usb0_vbus_det-gpios = <&pio 7 6 GPIO_ACTIVE_HIGH>; /* PH6 */
usb0_vbus-supply = <>; /* Remove or disable ID pin detection if it forces power-off */
usb1_vbus-supply = <&reg_usb1_vbus>;
};

mfg winfried

[LubOlimex]

Tested solution: A64-OLinuXino-1Ge4GW USB OTG with OLIMAGE

We reproduced the problem on A64-OLinuXino-1Ge4GW with kernel 5.10.180-olimex and found the cause.

It is possible to restore safe dual-role operation without rebuilding the complete image. We tested both USB-device mode and USB-host mode.

What is wrong

USB0 PHY0 is shared by MUSB, EHCI0 and OHCI0. The current device tree assigns PHY0 to all three controllers. During boot, EHCI0/OHCI0 requests host mode for PHY0. The sun4i PHY driver then stops following the USB0 ID pin, so normal OTG role switching fails.

The device-tree correction is:

• MUSB remains connected to PHY0 and remains in "otg" mode.
• The "phys" and "phy-names" properties are removed only from EHCI0 and OHCI0.
• The USB0 VBUS regulator is not forced permanently on.

Installation

Download install-a64-olinuxino-usb0-dual-role.sh. Log in as root and run:

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cd /root
wget https://ftp.olimex.com/TEMP/A64-OTG-fix/install-a64-olinuxino-usb0-dual-role.sh
chmod 700 /root/install-a64-olinuxino-usb0-dual-role.sh
/root/install-a64-olinuxino-usb0-dual-role.sh

If the script reports that the DTB was installed and the FIT image was rebuilt, disconnect everything from the micro-USB socket and reboot:

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reboot

The script verifies the board, creates backups, modifies and checks a temporary DTB, installs it, and rebuilds /boot/kernel.itb.

It also generates the complete readable DTS here:

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/root/sun50i-a64-olinuxino-1Ge4GW-usb0-dual-role.dts

Generating the full DTS from the installed DTB is safer than distributing one hard-coded DTS, since phandles and other definitions can change between OLIMAGE kernel packages.

Important limitation

For the moment, boot with the micro-USB socket empty. After Linux has started, insert the OTG adapter.

If the adapter is already inserted during boot, the kernel detects the host role but does not initially enable VBUS. Removing and reinserting the adapter fixes it. This remaining boot-time problem requires a small MUSB driver correction; it cannot be fixed completely by the DTS alone.

Test results

• Normal cable to a PC: USB peripheral mode worked, and the board did not drive VBUS.
• OTG adapter inserted after boot: host mode selected and VBUS enabled automatically.
• Low-speed USB mouse enumerated through OHCI0.
• High-speed SanDisk flash drive enumerated through EHCI0 as /dev/sda.
• Removing the OTG adapter disabled VBUS and returned USB0 to the idle role.

Quick check

With the OTG socket empty:

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cat /sys/class/extcon/extcon0/state

Expected result:

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USB=0
USB-HOST=0

After Linux has booted, insert the OTG adapter and check:

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cat /sys/class/extcon/extcon0/state
lsusb -t
dmesg | tail -n 30

The attached detailed guide contains the manual procedure and recovery commands.

Permanent OLIMAGE fix

The OLIMAGE kernel package should eventually include both corrections:

• Remove the EHCI0/OHCI0 PHY0 claims from the A64-OLinuXino device tree, leaving MUSB responsible for PHY0.
• Make the sunxi MUSB driver synchronize the existing USB-HOST extcon state when it starts, so booting with an OTG adapter already inserted also works.

After that, users should receive the complete fix normally through apt update, apt dist-upgrade, u-boot-install and reboot.

Until the fix is included in OLIMAGE, a future kernel package upgrade can replace the manually corrected DTB, in which case the workaround must be applied again.