Re: Is a multiplexer using latches a gpio controller?

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Tue, Jul 19, 2022 at 12:05 AM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
>
> 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?

It needs "downstream" GPIO and ->get_direction(), etc should act accordingly.

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

-- 
With Best Regards,
Andy Shevchenko