Re: [PATCH 0/2] pinctrl: zynqmp: Support muxing individual pins

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Fri, May 3, 2024 at 6:22 PM Sean Anderson <sean.anderson@xxxxxxxxx> wrote:

> This series adds support for muxing individual pins, instead of
> requiring groups to be muxed together. See [1] for additional
> discussion.
>
> [1] https://lore.kernel.org/linux-arm-kernel/5bb0dc7e-4c89-4f3d-abc6-41ae9ded5ae9@xxxxxxxxx/

The way I usually would recommend to solve this would be to
define new subgroups, so e.g. for a UARTS:

uart0_grp = pin_rx, pin_tx, pin_cts, pin_dts, pin_dcd;

And today this would be used like that:

mux0:
    function = "uart0";
    groups = "uart0_grp";

Then we realize that not everyone need all the modem
control signals provided. What to do. Well this:

uart0_rxtx_grp = pin_rx, pin_tx:
uart0_modem_grp = pin_cts, pin_dts, pin_dcd;

mux0:
    function = "uart0";
    groups = "uart0_rxtx_grp";

Now the CTS, DTS, DCD pins can be reused for something
else such as GPIO.

I *know* that this breaks ABI: the driver group definitions change
and the device tree needs to be changed too.

This only matters if the users have a habit of distributing the
kernel and DTB separately so a new kernel needs to support
and old DTB. This varies in how much control we have but I
think for Xilinx systems the kernel and DTB are always updated
in lockstep, so it really does not matter?

Yours,
Linus Walleij