linux-kernel - Re: [PATCH v2 1/5] dt-bindings: display: simple-framebuffer: Add interconnects property

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Message-ID: <20250703-light-baboon-of-experiment-179ca3@houat>
Date: Thu, 3 Jul 2025 11:41:44 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Hans de Goede <hdegoede@...hat.com>
Cc: Thomas Zimmermann <tzimmermann@...e.de>, 
	Krzysztof Kozlowski <krzk@...nel.org>, Luca Weiss <luca.weiss@...rphone.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Javier Martinez Canillas <javierm@...hat.com>, Helge Deller <deller@....de>, linux-fbdev@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] dt-bindings: display: simple-framebuffer: Add
 interconnects property

On Thu, Jul 03, 2025 at 10:34:23AM +0200, Hans de Goede wrote:
> Hi Thomas,
> 
> On 3-Jul-25 8:47 AM, Thomas Zimmermann wrote:
> > Hi
> > 
> > Am 02.07.25 um 22:43 schrieb Krzysztof Kozlowski:
> >> On 30/06/2025 10:40, Hans de Goede wrote:
> >>>> No one asks to drop them from the driver. I only want specific front
> >>>> compatible which will list and constrain the properties. It is not
> >>>> contradictory to your statements, U-boot support, driver support. I
> >>>> really do not see ANY argument why this cannot follow standard DT rules.
> >>> So what you are saying is that you want something like:
> >>>
> >>> framebuffer0: framebuffer@...85000 {
> >>>     compatible = "qcom.simple-framebuffer-sm8650-mdss", "simple-framebuffer";
> >>> }
> >>>
> >>> and that the binding for qcom.simple-framebuffer-sm8650-mdss
> >>> can then list interconnects ?
> >> IMO yes (after adjusting above to coding style), but as mentioned in
> >> other response you can just get an ack or opinion from Rob or Conor.
> > 
> > But does that work with *any* device that requires interconnects? The next such simple-framebuffer device should work out of the box *without* the kernel knowing anything about it. That's one of the key features of the simple-framebuffer.  If we have to maintainer per-device feature sets, it breaks that assumption.
> 
> The driver code for this can still be generic and since the driver
> will bind to the fallback plain "simple-framebuffer" compatible
> this should also work for new platforms.
> 
> The e.g. "qcom.simple-framebuffer-sm8650-mdss" compatible would
> purely be something in the dt-bindings to document which simplefb
> implementations will have interconnects and which ones will not.
> 
> The driver does not necessarily need to check these more
> precise compatibles, it can still just check for the generic
> presence of interconnects.

This ship has kind of sailed though. This binding has been used by
plenty of firmwares and bootloaders over the years, and has been
deployed on plenty of devices already.

Good luck fixing it in all of them, and then updating every device.

Maxime

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