TL-WR842ND V2 no USB power after switching to ATH79

For Developers
1

After building on ATH79 target there is no power on USB port. On AR7xxx/AR9xxx target it is working. I know it is something wrong with GPIO`s config. I am on the latest snapshot.
Ask me if any additional info is needed.

Thanks

2

Are you comfortable with command-line use of your device?

Someone would need to confirm that

#define TL_MR3420V2_GPIO_USB_POWER 4

is correct, based on

commit 3f7908d697
Author: Matthias Schiffer <redacted>
Date:   Wed Jan 31 21:18:16 2018 +0100

    ar71xx-generic: enable ATH79_MACH_TL_WR841N_V8 machine
    
    This machfile also contains the code for the TL-WR842N/ND v2, which is in
    ar71xx-generic and not in ar71xx-tiny.
[...]
3

Of course I am. How would I check that commit?

4

Ah, not that commit -- that is what led me to it being the WR841N_V8 to look at for the "old" GPIO definition.

The following should let you manually toggle a GPIO:

cd /sys/class/gpio/
echo 4 > export
cd gpio4
cat direction           # probably "in"
echo out > direction    # assuming set for "in"
cat value               # probably 0
echo 1 > value          # assuming was 0 before

If that resolves the problem, the changes to the DTS for ath79 should be straightforward (as would be a "quick hack" for your running device).

Please ask if you have any questions as to what the above is doing

5 
root@OpenWrt:/sys/class/gpio# echo 4 > export
ash: write error: Resource busy

root@OpenWrt:/sys/class/gpio# ls
export             gpiochip0          tp-link:power:usb  unexport

Hmm...

6

Looks like something is already using that GPIO -- hmmm...

target/linux/ath79/dts/ar9341_tplink_tl-wr842n-v2.dts

        gpio-export {
                compatible = "gpio-export";

                gpio_usb_power {
                        gpio-export,name = "tp-link:power:usb";
                        gpio-export,output = <1>;
                        gpios = <&gpio 4 GPIO_ACTIVE_HIGH>;
                };
        };

Looks like it's already exported by the above. That's a functional, but now-deprecated way of handling it.

Do you already have /sys/class/gpio/tp-link:power:usb/ on your running device?

If so, you should be able to continue with checking its behavior with

cd /sys/class/gpio/tp-link:power:usb/
cat direction           # should already be "out" based on the DTS
cat value               # probably 0
echo 1 > value          # toggle it, assuming was 0 before
7

cd /sys/class/gpio/tp-link:power:usb/

Seems to be a symlink to:

/sys/devices/platform/ahb/ahb:apb/18040000.gpio/gpiochip0/gpio/tp-link:power:usb

root@OpenWrt:/sys/devices/platform/ahb/ahb:apb/18040000.gpio/gpiochip0/gpio/tp-link:power:usb# ls
active_low device subsystem uevent value

8

You should be able to look at the current value and toggle it to see if you get USB power and, if so, what value is needed.