linux-kernel - Re: [PATCH 1/3] dt-bindings: auxdisplay: hit, hd44780: drop redundant GPIO node

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Date: Mon, 12 Feb 2024 14:38:27 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Ralf Schlatterbeck <rsc@...tux.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
 Linus Walleij <linus.walleij@...aro.org>, Miguel Ojeda <ojeda@...nel.org>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Robin van der Gracht
 <robin@...tonic.nl>, Paul Burton <paulburton@...nel.org>,
 linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 1/3] dt-bindings: auxdisplay: hit, hd44780: drop redundant
 GPIO node

On 12/02/2024 12:58, Ralf Schlatterbeck wrote:
> On Mon, Feb 12, 2024 at 12:25:48PM +0100, Krzysztof Kozlowski wrote:
>>
>> Hm, I don't understand how exactly it helps. The GPIO expander has its
>> own example and as you pointed below, this is basically the same code,
>> except rw and backlight GPIOs.
> 
> The hd44780 is a display that is very often used.
> By people (like me some time ago) not familiar with the nice io expander
> implementation in Linux. The consequence of that is that you'll find
> several out-of-tree implementations for this display with i2c out in the
> wild. So my thought of documenting this (again) at that location is to
> make it easier for people with a hd44780 with the standard i2c interface
> to see how it is done in Linux.

GPIO expanders and their usage is nothing specific to this device -
other devices also might benefit of them. Or the SoCs which have enough
of GPIOs... I really do not understand why do we need expander here and
how does it help

Anyway, binding examples should not be collection of unrelated
solutions, because then we should accept for each device schema several
other variations and combinations.

Best regards,
Krzysztof