Re: Is a multiplexer using latches a gpio controller?

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Mon, Jul 18, 2022 at 10:27 PM Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> we have a customer board here that uses two 8 port latches to drive
> LEDs. The setup looks as follows:
>
> CLK0 ----------------------.        ,--------.
> CLK1 -------------------.  `--------|>    #0 |
>                         |           |        |
> IN0 -----------------+--|-----------|D0    Q0|-----|◁
> IN1 ---------------+-|--|-----------|D1    Q1|-----|◁
> IN2 -------------+-|-|--|-----------|D2    Q2|-----|◁
> IN3 -----------+-|-|-|--|-----------|D3    Q3|-----|◁
> IN4 ---------+-|-|-|-|--|-----------|D4    Q4|-----|◁
> IN5 -------+-|-|-|-|-|--|-----------|D5    Q5|-----|◁
> IN6 -----+-|-|-|-|-|-|--|-----------|D6    Q6|-----|◁
> IN7 ---+-|-|-|-|-|-|-|--|-----------|D7    Q7|-----|◁
>        | | | | | | | |  |           `--------'
>        | | | | | | | |  |
>        | | | | | | | |  |           ,--------.
>        | | | | | | | |  `-----------|>    #1 |
>        | | | | | | | |              |        |
>        | | | | | | | `--------------|D0    Q0|-----|◁
>        | | | | | | `----------------|D1    Q1|-----|◁
>        | | | | | `------------------|D2    Q2|-----|◁
>        | | | | `--------------------|D3    Q3|-----|◁
>        | | | `----------------------|D4    Q4|-----|◁
>        | | `------------------------|D5    Q5|-----|◁
>        | `--------------------------|D6    Q6|-----|◁
>        `----------------------------|D7    Q7|-----|◁
>                                     `--------'
>
>
> So to change output 2 of latch #1 you have to apply the changed level on
> IN2, apply the previous level on the other inputs (to keep the other
> outputs constant) and toggle CLK1 once.
>
> This way you can drive 16 LEDs (or in general outputs) using only 10
> GPIOs. (And with a higher number of latches the proportion becomes a bit
> more useful.)
>
> Actually this construct is a general GPO (no input :-) controller, and I
> wonder if you would accept a driver that models it as a gpio controller.
>
> The dt binding could look as follows:
>
> latch-gpo {
>         compatible = "latch-gpo";
>         pinctrl-0 = <...>;
>         pinctrl-names = <...>;
>
>         clk-gpios = /* CLK0 */ <...>, /* CLK1 */ <...>;
>         data-gpios = /* IN0 */ <...>, /* IN1 */ <...>, ...;
> };
>
> What do you think?

Bart, what happened to the [1]? Is it abandoned, forgotten?

Uwe, isn't it what you need?

[1]: https://lore.kernel.org/linux-gpio/20220205215918.8924-1-maukka@xxxxxxxxxxxx/

-- 
With Best Regards,
Andy Shevchenko