Re: [PATCH v2 0/2] watchdog: realtek-otto: add fallback compatible

[Sander Vanheule]

On Thu, 2026-05-14 at 11:10 -0500, Rob Herring wrote:
> On Tue, May 12, 2026 at 10:48:52PM +0200, Sander Vanheule wrote:
> > Like for the GPIO hardware of the Realtek Otto platform, add a fallback
> > compatible for the watchdog hardware.
> > 
> > For backward compatibility, the binding will still allow current
> > single-compatible devicetrees to work, but new devicetrees, including
> > new compatibles, should use a two-component compatible.
> > 
> > This series serves to address comments regarding the device compatibles
> > for the patches adding RTL9607C watchdog support [1].
> > 
> > [1] https://lore.kernel.org/lkml/20260509163101.722793-1-adilov@xxxxxxxxxxx/
> 
> You misunderstood the discussion (though some came after this). The 
> fallback should be one of the existing compatibles (the oldest one), so 
> there are no driver changes needed for the OS. Creating a new fallback 
> completely misses that point.

Using a SoC-specific compatible would mean we should go for something like:
	compatible = "realtek,rtl9706c-wdt", "realtek,rtl8380-wdt";

Then that means we can never change our interpretation of how the rtl8380
behaves (we don't have datasheets), because it would also impact the behavior of
the rtl9706c.

I also think "apple,wdt" is a bad example to compare with "realtek,otto-wdt".
The former only specifies the vendor, while the latter refers to the line of
SoCs this IP block is used for. Although I see the docs also discourage family
compatibles.

If I may ask, what is the rationale for preferring the "older implementation"
approach over a "family compatible" to match the common subset of supported
features?

Best,
Sander