linux-kernel - Re: [PATCH v2 4/5] dt-bindings: auxdisplay: Add bindings for Hitachi HD44780

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Date:   Mon, 20 Mar 2017 10:15:16 -0500
From:   Rob Herring <robh@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Willy Tarreau <willy@...roxy.com>,
        Ksenija Stanojevic <ksenija.stanojevic@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Akira Tsukamoto <akira.tsukamoto@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] dt-bindings: auxdisplay: Add bindings for Hitachi
 HD44780

On Fri, Mar 10, 2017 at 03:15:20PM +0100, Geert Uytterhoeven wrote:
> Add DT bindings for an Hitachi HD44780 Character LCD Controller where
> its M6800 bus interface is connected to GPIOs.
> 
> Memory-mapped configurations are not yet supported.
> 
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> Memory-mapped configurations can be supported by amending the binding to
> make mandatory either the {data,enable,rs}-gpios properties, or a "reg"
> (and optional "reg-names") property.
> 
> As the driver doesn't support this yet, and there are different ways to
> organize the register map (some wirings use different addresses for
> reading and writing, to simplify bus glue logic), this is left for a
> future improvement.
> 
> v2:
>   - Added rationale below "---".
> ---
>  .../devicetree/bindings/auxdisplay/hit,hd44780.txt | 44 ++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt
> 
> diff --git a/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt b/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt
> new file mode 100644
> index 0000000000000000..ee4054da458d412f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt
> @@ -0,0 +1,44 @@
> +DT bindings for the Hitachi HD44780 Character LCD Controller
> +
> +The Hitachi HD44780 Character LCD Controller is commonly used on character LCDs
> +that can display one or more lines of text. It exposes an M6800 bus interface,
> +which can be used in either 4-bit or 8-bit mode.
> +
> +Required properties:
> +  - compatible: Must contain "hit,hd44780",
> +  - data-gpios: Must contain an array of either 4 or 8 GPIO specifiers,
> +    referring to the GPIO pins connected to the data signal lines DB0-DB7
> +    (8-bit mode) or DB4-DB7 (4-bit mode) of the LCD Controller's bus interface,
> +  - enable-gpios: Must contain a GPIO specifier, referring to the GPIO pin
> +    connected to the "E" (Enable) signal line of the LCD Controller's bus
> +    interface,
> +  - rs-gpios: Must contain a GPIO specifier, referring to the GPIO pin
> +    connected to the "RS" (Register Select) signal line of the LCD Controller's
> +    bus interface,
> +  - display-height: Height of the display, in character cells,
> +  - display-width: Width of the display, in character cells.

display-{width,height}-chars

> +
> +Optional properties:
> +  - rw-gpios: Must contain a GPIO specifier, referring to the GPIO pin
> +    connected to the "RW" (Read/Write) signal line of the LCD Controller's bus
> +    interface,
> +  - backlight-gpios: Must contain a GPIO specifier, referring to the GPIO pin
> +    used for enabling the LCD's backlight,

Active state?

> +  - internal-buffer-width: Internal buffer width (default is 40 for displays
> +    with 1 or 2 lines, and display-width for displays with more than 2 lines).
> +
> +Example:
> +
> +	auxdisplay {
> +		compatible = "hit,hd44780";
> +
> +		data-gpios = <&hc595 0 GPIO_ACTIVE_HIGH>,
> +			     <&hc595 1 GPIO_ACTIVE_HIGH>,
> +			     <&hc595 2 GPIO_ACTIVE_HIGH>,
> +			     <&hc595 3 GPIO_ACTIVE_HIGH>;
> +		enable-gpios = <&hc595 4 GPIO_ACTIVE_HIGH>;
> +		rs-gpios = <&hc595 5 GPIO_ACTIVE_HIGH>;
> +
> +		display-height = <2>;
> +		display-width = <16>;
> +	};
> -- 
> 2.7.4
>