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

On Mon, Jun 30, 2025 at 10:24:06AM +0200, Krzysztof Kozlowski wrote:

On 29/06/2025 14:07, Hans de Goede wrote:

quoted

Hi Krzysztof,

On 28-Jun-25 1:49 PM, Krzysztof Kozlowski wrote:

quoted

On 27/06/2025 11:48, Luca Weiss wrote:

quoted

Hi Krzysztof,

On Fri Jun 27, 2025 at 10:08 AM CEST, Krzysztof Kozlowski wrote:

quoted

On Mon, Jun 23, 2025 at 08:44:45AM +0200, Luca Weiss wrote:

quoted

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@suse.de>
Signed-off-by: Luca Weiss <redacted>
---
 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?

And IMO they should not. Bindings are not supposed to be generic.

The simplefb binding is a binding to allow keeping the firmware, e.g.
uboot setup framebuffer alive to e.g. show a boot splash until
the native display-engine drive loads. Needing display-engine
specific bindings totally contradicts the whole goal of 

No, it does not. DT is well designed for that through expressing
compatibility. I did not say you cannot have generic fallback for simple
use case.

But this (and previous patchset) grows this into generic binding ONLY
and that is not correct.

Can we have a proper definition of what a correct device tree binding is
then?

It's a bit surprising to have *that* discussion over a binding that is
now well older than a decade now, and while there is definitely some
generic bindings in ePAPR/DT spec, like the CPU ones.

If you don't consider that spec to be correct DT bindings, please
provide a definition of what that is, and / or reasonable alternatives.

Also, no, a device specific binding isn't reasonable here, because we
*don't* have a device. From a technical standpoint, the firmware creates
the framebuffer, Linux just uses it. Just like you don't have a
device/platform specific compatible for PSCI, SCPI, et al.

And from a process standpoint, that driver is typically used years
before we even get to writing a driver for the actual display driver.
And since bindings are far from standard and actually pretty
opionionated, even if we submitted a binding to use a proper binding
without having a clear idea of what the hardware is, or what a driver
would want, we would end up with either a broken binding, or a broken
driver.

Maxime