mt7621 GPIO mapping mystery

Fri Jan 20 23:56:15 PST 2023

Hi,

On Sat, Jan 21, 2023 at 7:03 AM Arınç ÜNAL <arinc.unal at arinc9.com> wrote:
>
> Pins from 22 to 33 are on the rgmii2 pin group. They don't function as
> GPIO by default. Requesting a gpio by either from devicetree or `echo
> 203 >  /sys/class/gpio/export` won't change anything. You have to claim
> the pin group as gpio on the devicetree.

Yes, you have to claim the pin group as gpio on the device tree to
make this work. Ralink has the concept of "GPIO mode" but actually is
just an electrical configuration for a certain device. So if the mode
(function) is not requested as a real GPIO nothing is going to work.
So in your board's dts file you have to add something like the
following with the groups you want to claim as real gpio function:

#include "mt7621.dtsi"
...

&state_default {
    gpio {
        groups = "jtag", "uart3", "wdt";
        function = "gpio";
    };
};

>
> Quoting my response from [0]:
>
> > state_default is there to explicitly set the function of a pin group to gpio, this is done because the bootloader may have set the function of a pin group to something else before booting OpenWrt which would render the pins of that group uncontrollable for general purpose aka GPIO.
> >
> >     Actually I think @arinc9 did some work around that.
> >
> > Not yet, I plan to modify the gpio_request_enable pinmux operation to set the pin group as gpio when there's a gpio request for a pin in that pin group. gpio_request_enable pinmux operation can only set the function of an individual pin currently. Since ralink pinctrl driver can only set the function of a group of pins, the operation currently cannot be used.
> >
> > If we make it work, any GPIO defined on devicetree or exported from userspace will automatically have the function of the pin group it's in set to gpio, completely getting rid of the need for explicitly defining functions of certain pin groups on the devicetree.
>
> Of course when I said "I plan to modify this code" I actually meant I
> was going to talk this through with Sergio but I never had the
> opportunity to do so. I guess this thread is a good place to start
> talking about this.
>
> I had this case on a user:
>
> They got an LED wired to wdt pin. GPIO is already exported on the DT.
> However their LED just won't work.
>
> It turns out the bootloader sets the wdt pin's function to something
> other than gpio. And when OpenWrt boots, the pinctrl driver makes no
> changes to the pin's function.

Bootloader always sets its own configuration for the pinctrl. The
linux pinctrl driver sets every single group default mode [0] as it is
in the Mediatek's Mt7621 datasheet.

>
> So we had to specifically claim that pin as gpio to make the LED work.
> Now there is already a solution for this which is the
> gpio_request_enable pinmux operation but it's not supposed to be used on
> pinctrl drivers that cannot control pins individually.
>
> Sergio, you think we can somehow make this pinmux operation mux a pin
> group as gpio instead of a single pin?

I am not an expert in pinmux drivers but I think there are strong
reasons why only a single pin is allowed to be requested.

See kernel doc about this here: [1]

>
> Or introduce a new pinmux operation that can do this?

I think you should send an email to kernel gpio / pinctrl kernel mail
list to get feedback from Bart and Linus as gpio and pin control
maintainers to properly understand the way to go but I don't really
understand what is the problem requesting the group as gpio in the
device tree like any other single platform is doing and seems to be
the correct way to go. Maybe I am missing something :)

>
> [0] https://github.com/openwrt/openwrt/pull/4470#issuecomment-1243345944
>

Best regards,
    Sergio Paracuellos

[0]: https://elixir.bootlin.com/linux/v6.2-rc4/source/drivers/pinctrl/ralink/pinctrl-mt7621.c
[1]: https://www.kernel.org/doc/html/latest/driver-api/pin-control.html#pin-control-interaction-with-the-gpio-subsystem

> Arınç
>
> On 20.01.2023 22:24, Peter Naulls wrote:
> >
> >
> > I posted previously on GPIOs, which caused some debate; this may or may not
> > be relevant, but I'd be remiss to not mention it:
> >
> > http://lists.openwrt.org/pipermail/openwrt-devel/2022-October/039593.html
> >
> > I've been chasing an issue with GPIO mapping in for an mt7621 on the
> > OpenWrt
> > 5.10.161 etc kernels.
> >
> > In short, GPIOS up to at least 17 work, but 22 and beyond do not - 5-17
> > and 22-24 are LEDs, so their operation should be immediately obvious.
> > The are all active high and are all wired as you'd expect.
> >
> > This all works as expected on a previous 4.14 kernel.  To say that there
> > have been significant changes in drivers, GPIO handling and device tree
> > since
> > that kernel would be an understatement.
> >
> > I have tried exporting the GPIOS as LEDs, named GPIOs, direct
> > manipulation in
> > /sys/class/gpio and libgpiod, but something is amiss. The actual value
> > of the GPIO as seen in software can manipulated in all cases, but the
> > physical value
> > does not change.
> >
> > Suspiciously, MDIO/MDC are at GPIOs 20 and 21, so I don't know if these are
> > upsetting the physical mapping.  I've also turned off as much as
> > possible in
> > the device tree, and built the kernel without switch and ethernet
> > drivers, etc.
> >
> > I'm tearing my hair out here, so any clues at all would be appreciated.
> >
> > Thanks!
> >
> >
> >
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