linux-kernel - Re: [PATCH v4 1/3] dt-bindings: display: Add Sitronix ST7571 LCD Controller

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Message-ID: <Z_4RZdlV_OV1qLRj@gmail.com>
Date: Tue, 15 Apr 2025 09:57:25 +0200
From: Marcus Folkesson <marcus.folkesson@...il.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	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 v4 1/3] dt-bindings: display: Add Sitronix ST7571 LCD
 Controller

Hi Krzysztof,

On Tue, Apr 15, 2025 at 09:22:30AM +0200, Krzysztof Kozlowski wrote:
> On 15/04/2025 07:58, Marcus Folkesson wrote:
> > +title: Sitronix ST7571 Display Controller
> > +
> > +maintainers:
> > +  - Marcus Folkesson <marcus.folkesson@...il.com>
> > +
> > +description:
> > +  Sitronix ST7571 is a driver and controller for 4-level gray
> > +  scale and monochrome dot matrix LCD panels.
> > +
> > +allOf:
> > +  - $ref: panel/panel-common.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    const: sitronix,st7571
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  sitronix,grayscale:
> > +    type: boolean
> > +    description:
> > +      Display supports 4-level grayscale.
> 
> That's fully deducible from compatible, no? Or does it depend on actual
> panel, but then what else depends on the panel?

No it is not, the ST7571 is only the controller and some properties
depends on the connected LCD.

ST7571 supports both grayscale and monochrome LCDs but has no way to
know what is connected.

Other properties that depends on the LCD are:
panel-timing.hactive
panel-timing.vactive
panel-timing.vfront-porch

In the first revisons of the driver, I thought I could let the
grayscale and monochrome setting depends on which pixel format that
where used, but that was not the case.

> 
> Best regards,
> Krzysztof


Best regards,
Marcus Folkesson

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