* Stephen Warren wrote:

Thierry Reding wrote at Saturday, March 03, 2012 3:54 PM:

quoted

I'm confused. If I know exactly that the hardware is Tegra30 (which it
definitely should be if I include tegra30.dtsi), then why list "tegra20-pwm"
as compatible?

Or did you mean to list tegra30-pwm as compatible value in the PWM driver?

Standard practice is to list the exact model of the HW as the first entry
in compatible in the .dts file:

    nvidia,tegra30-pwm

This is so that the DT always describes exactly which HW model is actually
present, so that if HW-model-specific WARs/... are required in the future,
the DT already lists that information up-front.

Then additionally list any older HW models that this HW is also compatible
with:

    nvidia,tegra20-pwm


This allows the driver to list just nvidia,tegra20-pwm but still bind
to DT nodes that are for later HW.

So, in other words, you end up with the following in the .dts/.dtsi file:

    compatible = "nvidia,tegra30-pwm", "nvidia,tegra20-pwm";

Okay, that makes sense now. For some reason I thought you were suggesting to
put the same into tegra20.dtsi as well. I'll add nvidia,tegra30-pwm to the
compatible list in the driver and list both values in the tegra30.dtsi.
Thanks for explaining.

quoted

quoted

Could you also write binding documentation, in particular explaining
what the two pwm-cells are specifically for Tegra:

Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt

(although perhaps that'd be part of the previous patch which implements
the driver)

Actually for Tegra the values would be those documented in the generic
binding because Tegra uses of_pwm_simple_xlate(). Does it still make sense to
add a Tegra-specific binding?

There should still be a Tegra-specific binding. Without it, there's no
definite way to know whether the "standard" properties actually apply,
or someone simply forgot to document it.

Understood. I assume that both the Tegra20 and Tegra30 variants should have
explicit bindings then as well, right?

Thierry