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

[Thomas Zimmermann]

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@xxxxxxx>
> > > > Signed-off-by: Luca Weiss <luca.weiss@xxxxxxxxxxxxx>
> > > > ---
> > > >    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)