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

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Message-ID: <b94b752c-d7f7-41d6-ac79-d21427f20964@kernel.org>
Date: Sat, 28 Jun 2025 13:50:40 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Thomas Zimmermann <tzimmermann@...e.de>,
 Luca Weiss <luca.weiss@...rphone.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
 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

On 27/06/2025 13:34, Thomas Zimmermann wrote:
> Hi
> 
> Am 27.06.25 um 10:08 schrieb Krzysztof Kozlowski:
>> On Mon, Jun 23, 2025 at 08:44:45AM +0200, Luca Weiss wrote:
>>> Document the interconnects property which is a list of interconnect
>>> paths that is used by the framebuffer and therefore needs to be kept
>>> alive when the framebuffer is being used.
>>>
>>> Acked-by: Thomas Zimmermann <tzimmermann@...e.de>
>>> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>>> ---
>>>   Documentation/devicetree/bindings/display/simple-framebuffer.yaml | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/display/simple-framebuffer.yaml b/Documentation/devicetree/bindings/display/simple-framebuffer.yaml
>>> index 296500f9da05e296dbbeec50ba5186b6b30aaffc..f0fa0ef23d91043dfb2b220c654b80e2e80850cd 100644
>>> --- a/Documentation/devicetree/bindings/display/simple-framebuffer.yaml
>>> +++ b/Documentation/devicetree/bindings/display/simple-framebuffer.yaml
>>> @@ -79,6 +79,9 @@ properties:
>>>     power-domains:
>>>       description: List of power domains used by the framebuffer.
>>>   
>>> +  interconnects:
>>> +    description: List of interconnect paths used by the framebuffer.
>>> +
>> maxItems: 1, or this is not a simple FB anymore. Anything which needs
>> some sort of resources in unknown way is not simple anymore. You need
>> device specific bindings.
> 
> In this context, 'simple' means that this device cannot change display 
> modes or do graphics acceleration. The hardware itself is not 
> necessarily simple. As Javier pointed out, it's initialized by firmware 

If hardware is not simple, then it needs specific bindings.

> on the actual hardware. Think of 'VGA-for-ARM'. We need these resources 
> to keep the display working.

I don't claim you do not need these resources. I claim device is not
simple thus does not suit rules for generic bindings. Generic bindings
are in general not allowed and we have them only for very, very simple
devices.

You say this is not simple device, so there you go - specific binding
for this complex (not-simple) device.

Best regards,
Krzysztof