linux-kernel - Re: [PATCH 1/2] dt-bindings: display: Add Sharp Memory LCD bindings

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Message-ID: <8edc9bd6-2130-44aa-aeaf-cfb5ca43ca0f@kernel.org>
Date: Sun, 28 Jul 2024 16:43:42 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Alex Lanzano <lanzano.alex@...il.com>
Cc: mehdi.djait@...tlin.com,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, dri-devel@...ts.freedesktop.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: display: Add Sharp Memory LCD bindings

On 28/07/2024 14:56, Alex Lanzano wrote:
>>>>> +
>>>>> +  spi-cs-high: true
>>>>
>>>> You can drop it.
>>>>
>>>
>>> This is a required property in order for the display to function correctly.
>>> But I have no issues removing it if there's a better place to document it.
>>
>> The sharp LCD device or the board (e.g. via some inversion)?
>>
> 
> The sharp LCD device itself.
> 
> https://cdn.sparkfun.com/assets/d/e/8/9/7/LS013B7DH03_datasheet.pdf
> Page 16 of the PDF below shows the timing chart for it if interested

OK, so you enforce chip select as always high and then someone comes
with a board which has a inversion and expect the SoC to drive it low,
as usually? In such system this would not work, would it?

IOW, I think this is the first case where you require specific CS high
and this should make you think why...

Best regards,
Krzysztof