Configuring the I2C clock on the ODROID C2

[Vincent DEFERT <vincent.defert%posteo.net@localhost>]

Hi,

I'm testing my I2C driver for the ODROID C2 and it fails to get the I2C 
peripheral clock.

In meson-gxbb.dtsi, I have:

    &i2c_A {
        clocks = <&clkc CLKID_I2C>;
    };

and CLKID_I2C is defined as 22 in dt-bindings/clock/gxbb-clkc.h.
No clock-name is defined for this clock in the DTS.

My understanding is that the I2C peripheral shares the same clock as 
many other peripherals and CLKID_I2C is only used for clock gating.
At least, it's what I guess from the very superficial public data sheet 
given by HardKernel.

However, I need to first enable it, then determine this clock's 
frequency in order to calculate the division factor to generate a proper 
I2C SCK signal.

I sought inspiration in rk_i2c.c and did this:

    sc->sc_sclk = fdtbus_clock_get(phandle, "xtal");

    if (sc->sc_sclk == NULL) {
        aprint_error(": couldn't get CLKID_I2C\n");
        return;
    } else if (clk_enable(sc->sc_sclk) != 0) {
        aprint_error(": couldn't enable CLKID_I2C\n");
        return;
    }

"xtal" is the clock name I found in the definition of clkc.
Result: sc->sc_sclk == NULL

Then, I replaced the fdtbus_clock_get line with:

sc->sc_sclk = fdtbus_clock_get_index(phandle, 22);

22 being the value found in dt-bindings/clock/gxbb-clkc.h.
Result: sc->sc_sclk == NULL

Obviously, my guessing engine performs very poorly on this problem and I 
could use some help. :)

Vincent