On Fri, 28 Oct 2022 11:34:16 +0100, Aidan MacDonald wrote:
The AIC needs only the first two clocks: "aic" is a gate that's used for gating the I2S controller when it's suspended, and "i2s" is the system clock, from which the bit and frame clocks are derived. Both clocks are therefore reasonably part of the AIC and should be passed to the OS.
But the "ext" and "pll half" clocks are a little more questionable. It appears these bindings were introduced when the schema was first converted to YAML, but weren't present in the original .txt binding. They are intended to be the possible parent clocks of "i2s".
The JZ4770 actually has three parents for its "i2s" clock, named "ext", "pll0", and "pll1" in the Linux driver. The JZ4780 has two parents but it doesn't have a "pll half" clock, instead it has an "i2s_pll" clock which behaves much differently to the actual "pll half" clock found on the JZ4740 & JZ4760. And there are other Ingenic SoCs that share the JZ4780's clock layout, eg, the X1000.
Therefore, the bindings aren't really adequate for the JZ4770 and a bit misleading for the JZ4780. Either we should fix the bindings, or remove them entirely.
This patch opts to remove the bindings. There is a good case to be made that "ext" and "pll half" don't belong here because they aren't directly used by the AIC. They are only used to set the parent of the "i2s" clock; they have no other effect on the AIC.
A good way to think of it is in terms of how the AIC constrains clocks. The AIC can only generate the bit & frame clocks from the system clock in certain ratios. Setting the sample rate effectively constrains the frame clock, which, because of the clock dividers controlled by the AIC, translates to constraints on the "i2s" clock. Nothing in the AIC imposes a direct constraint on the parents of the "i2s" clock, and the AIC does not need to enable or disable the parents directly, so in principle the AIC doesn't need to be aware of the parent clocks at all.
The choice of parent clock is still important, but the AIC doesn't have enough information to apply such constraints itself. The sound card does have that information because it knows how the AIC is connected to other components. We need to use other DT mechanisms to communicate those constraints at the sound card level, instead of passing the clocks through to the AIC, and inventing ad-hoc ways to plumb the constraints around behind the scenes.
Signed-off-by: Aidan MacDonald aidanmacdonald.0x0@gmail.com
.../devicetree/bindings/sound/ingenic,aic.yaml | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-)
Acked-by: Rob Herring robh@kernel.org