[RFC] ARM: dts: Add i2cmux-pinctrl config to Raspberry Pi i2c-0

[Stefan Wahren]

Hi Dave,

> Dave Stevenson <dave.stevenson at raspberrypi.org> hat am 20. November 2017 um 15:09 geschrieben:
> 
> 
> The first i2c controller on the Raspberry Pi family can
> be pinmuxed to either GPIOs 0&1, 28&29, or 44&45.
> The default has always been 0&1 as those are exposed on
> the 40 pin GPIO header of the more recent models.
> GPIOs 28&29 on Pi 0/1/2/3 and GPIOs 44&45 on Pi3 are
> used for i2c to the DSI display and the camera module.
> 
> The i2c-mux-pinctrl driver allows pinctrl setup to be used
> to expose the GPIO sets as alternate i2c adapters. This
> patch configures that driver to expose two adapters -
> i2c0 on GPIOs 0&1, and i2c_csi_dsi on the correct GPIOs for
> the camera and display.
> (This could be extended to expose all 3 options on the CM
> and CM3, but there isn't a pressing case for that at present).
> 
> The one quirk with the i2cmux-pinctrl driver is that the
> parent controller still exists as an i2c adapter which
> will be connnected to whichever pins were last requested
> (or an optional idle setting). That adapter appears first so
> is numbered as adapter 0, whilst the child ports end up as
> adapters 3&4. These can be renumbered through using DT aliases
> if we wish to retain the ordering of adapters (this will be
> required downstream).
> 
> Signed-off-by: Dave Stevenson <dave.stevenson at raspberrypi.org>
> ---
> 
> Hi All.
> 
> Thoughts from people?
> Do others care about access to the alternate pin muxing options for BSC0?
> Is the location of these changes acceptable?
> Objections on naming of nodes?

i'm not sure that i understood complete issue. This seems to be a RPi specific problem.
So you want to add a new driver for a "virtual" muxing in order to use csi/dsi?

Do you think the issue could be fixed with the following DT part (example)

&i2c0 {
        pinctrl-names = "default", "dsi_csi";
        pinctrl-0 = <&i2c0_gpio0>;
        pinctrl-1 = <&i2c0_gpio44>;
        compatible = "raspberrypi,bcm2835-i2c0";
        status = "okay";
        clock-frequency = <100000>;
};

and extending the i2c driver with the necessary pinctrl handling instead?