Re: [PATCH v1 2/5] pardata: new bus for parallel data access

From: Geert Uytterhoeven
Date: Mon Jan 20 2020 - 05:11:04 EST


Hi Sam,

(stumbled on this accidentally)

On Thu, Aug 2, 2018 at 9:46 PM Sam Ravnborg <sam@xxxxxxxxxxxx> wrote:
> The pardata supports implement a simple bus for devices
> that are connected using a parallel bus driven by GPIOs.
> The is often used in combination with simple displays
> that is often seen in older embedded designs.
> There is a demand for this support also in the linux
> kernel for HW designs that uses these kind of displays.
>
> The pardata bus uses a platfrom_driver that when probed
> creates devices for all child nodes in the DT,
> which are then supposed to be handled by pardata_drivers.
>
> Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx>

> --- /dev/null
> +++ b/Documentation/driver-api/pardata.rst
> @@ -0,0 +1,60 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========================
> +Parallel Data Bus/Drivers
> +=========================
> +
> +Displays may be connected using a simple parallel bus.
> +This is often seen in embedded systems with a simple MCU, but is also
> +used in Linux based systems to a small extent.
> +
> +The bus looks like this:
> +
> +.. code-block:: none
> +
> + ----+
> + | DB0-DB7 or DB4-DB7 +----
> + ===/========================
> + | E - enable | D
> + ---------------------------- I
> + C | Reset | S
> + P ---------------------------- P
> + U | Read/Write (one or two) | L
> + ---------------------------- A
> + | RS - instruction/data | Y
> + ----------------------------
> + | +----
> + ----+

Oh, cool! Looks like this can be used by the hd44780 driver.

Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt
drivers/auxdisplay/hd44780.c

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds