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

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Message-ID: <vk7xshncx3vj66ykbt3cfdjwdsx5uewfzlqmfsdbjfgju4awwk@lz76hnenxq2u>
Date: Sun, 6 Jul 2025 14:24:33 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Hans de Goede <hdegoede@...hat.com>, Luca Weiss <luca.weiss@...rphone.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>,
        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 Wed, Jul 02, 2025 at 10:43:27PM +0200, Krzysztof Kozlowski wrote:
> 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, this way we end up describing MDSS hardware block twice: once with
the proper device structure and once more in the simple-framebuffer
definition. I think this is a bit strange.

I understand your point of having a device-specific compatible string
and also having a verifiable schema, but I think it's an overkill here.

Consider regulator supplies of this simple-framebuffer. Obviously some
of them supply the panel and not the SoC parts. Should we also include
the panel into the respective compat string? What about describing the
device with two different DSI panels?

I think this explodes too quickly to be useful. I'd cast my (small) vote
into continuing using the simple-framebuffer as is, without additional
compatible strings and extend the bindings allowing unbound number of
interconnects.

-- 
With best wishes
Dmitry