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

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Message-ID: <87o6u9birl.fsf@minerva.mail-host-address-is-not-set>
Date: Fri, 27 Jun 2025 12:06:54 +0200
From: Javier Martinez Canillas <javierm@...hat.com>
To: Luca Weiss <luca.weiss@...rphone.com>, Krzysztof Kozlowski
 <krzk@...nel.org>
Cc: Hans de Goede <hdegoede@...hat.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, 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>, 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

"Luca Weiss" <luca.weiss@...rphone.com> writes:

> Hi Krzysztof,
>
> On Fri Jun 27, 2025 at 10:08 AM CEST, Krzysztof Kozlowski wrote:
>> 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.
>
> The bindings support an arbitrary number of clocks, regulators,
> power-domains. Why should I artificially limit the interconnects to only
> one?
>

I agree with Luca here. There are device specific bindings for the device
specific drivers. But this is about the generic drivers that are able to
scan out using a system provided framebuffer.

The display controller is setup by the firmware but it might need a set
of clocks, power domains, regulators, etc left enabled in order to work.

It's true that the "simple" is a misnomer, probably these drivers should
had been named sysfb and sysfbdrm, or something along those lines.

> The driver code also has that support added in this series.
>
> Regards
> Luca
>
>>
>> Best regards,
>> Krzysztof
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat