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

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Message-ID: <f5fe3fe1-903a-48ca-9249-b77bc07dbc77@redhat.com>
Date: Thu, 3 Jul 2025 10:34:23 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: Thomas Zimmermann <tzimmermann@...e.de>,
 Krzysztof Kozlowski <krzk@...nel.org>, Luca Weiss <luca.weiss@...rphone.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, 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

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.

Regards,

Hans