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

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Message-ID: <CAMuHMdVP4UwGYuNcOphPO9F2pSCaHS1j-ODxYrv_LNOoo_4coA@mail.gmail.com>
Date:   Mon, 20 Jan 2020 11:10:37 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Noralf T <noralf@...nnes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v1 2/5] pardata: new bus for parallel data access

Hi Sam,

(stumbled on this accidentally)

On Thu, Aug 2, 2018 at 9:46 PM Sam Ravnborg <sam@...nborg.org> 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@...nborg.org>

> --- /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@...ux-m68k.org

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