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Date:   Wed, 19 May 2021 13:54:51 +0200
From:   Ralf Schlatterbeck <rsc@runtux.com>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Rob Herring <robh@kernel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Willy Tarreau <w@1wt.eu>, Lars Poeschel <poeschel@lemonage.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>
Subject: Re: [PATCH 1/1] auxdisplay: Add I2C gpio expander example
Message-ID: <20210519115450.qoqpy7d5dgnjtenx@runtux.com>
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The hd44780 displays are often used with pcf8574 based I/O expanders.
Add example to documentation.

Signed-off-by: Ralf Schlatterbeck <rsc@runtux.com>
---
Updated Patch, thanks to Geert Uytterhoeven for his tip on how to
reproduce the warning. I've removed the address from the i2c stanza
which fixes it. Let me know if I should re-post the patch in a separate
thread.

 .../bindings/auxdisplay/hit,hd44780.yaml      | 31 ++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.yaml b/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.yaml
index 9222b06e93a0..fde07e4b119d 100644
--- a/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.yaml
+++ b/Documentation/devicetree/bindings/auxdisplay/hit,hd44780.yaml
@@ -12,7 +12,10 @@ maintainers:
 description:
   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.
+  interface, which can be used in either 4-bit or 8-bit mode. By using a
+  GPIO expander it is possible to use the driver with one of the popular I2C
+  expander boards based on the PCF8574 available for these displays. For
+  an example see below.
 
 properties:
   compatible:
@@ -94,3 +97,29 @@ examples:
             display-height-chars = <2>;
             display-width-chars = <16>;
     };
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    i2c {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            pcf8574: pcf8574@27 {
+                    compatible = "nxp,pcf8574";
+                    reg = <0x27>;
+                    gpio-controller;
+                    #gpio-cells = <2>;
+            };
+    };
+    hd44780 {
+            compatible = "hit,hd44780";
+            display-height-chars = <2>;
+            display-width-chars  = <16>;
+            data-gpios = <&pcf8574 4 0>,
+                         <&pcf8574 5 0>,
+                         <&pcf8574 6 0>,
+                         <&pcf8574 7 0>;
+            enable-gpios = <&pcf8574 2 0>;
+            rs-gpios = <&pcf8574 0 0>;
+            rw-gpios = <&pcf8574 1 0>;
+            backlight-gpios = <&pcf8574 3 0>;
+    };
-- 
2.20.1