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

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Message-ID: <f15a775d-d82f-4ac9-9d88-159ffcf7e81c@suse.de>
Date: Mon, 30 Jun 2025 08:34:25 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Krzysztof Kozlowski <krzk@...nel.org>,
 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

Hi

Am 28.06.25 um 13:50 schrieb Krzysztof Kozlowski:
> 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.

No, I didn't. I said that the device is simple. I did not say that the 
device's hardware is simple. Sounds nonsensical, but makes sense here. 
The simple-framebuffer is just the range of display memory that the 
firmware configured for printing boot-up messages. We use it for the 
kernel's output as well.  Being generic and simple is the exact raison 
d'etre for simple-framebuffer.  (The display property points to the 
actual hardware, but we don't need it.)

Best regards
Thomas

>
> Best regards,
> Krzysztof

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)