Hi Rob,

On 14. 12. 2021, at 16:40, Rob Herring [off-list ref] wrote:

On Tue, Dec 14, 2021 at 12:02:48PM +0000, Martin Povišer wrote:

quoted

The NCO block found on Apple SoCs is a programmable clock generator
performing fractional division of a high frequency input clock.

Signed-off-by: Martin Povišer <redacted>
---
.../devicetree/bindings/clock/apple,nco.yaml  | 70 +++++++++++++++++++
1 file changed, 70 insertions(+)
create mode 100644 Documentation/devicetree/bindings/clock/apple,nco.yaml

diff --git a/Documentation/devicetree/bindings/clock/apple,nco.yaml b/Documentation/devicetree/bindings/clock/apple,nco.yaml
new file mode 100644
index 000000000000..5029824ab179
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/apple,nco.yaml

@@ -0,0 +1,70 @@

quoted

+
+  apple,nchannels:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      The number of output channels the NCO block has been
+      synthesized for.

I'd assume there is some max number?

There might be some limit to the underlying IP but we wouldn’t know.
What we know about the hardware comes from blackbox reversing, and that
doesn't suggest a particular limit to the number of channels we might
see on the SoC block in future.

Do you really need to know this? If this is just to validate the clock
cell values are less than this, then just drop that and the property.
It's not the kernel's job to validate the DT.

Well strictly speaking the driver could do clock registration on-demand
at the cost of additional book-keeping, in which case we could drop
the property, but I would prefer we don’t do that. Rather than providing
validation the property simplifies drivers.

Another option is calculating the no. of channels from size of the reg
range, but I assume that’s worse than having the nchannels property.

quoted

+
+    nco: clock-generator@23b044000 {

clock-controller@...

Okay, will change.

quoted

+      compatible = "apple,t8103-nco", "apple,nco";
+      reg = <0x3b044000 0x14000>;

You really have 0x14000 worth of registers here because all of that
will be mapped into virtual memory? Doesn't matter so much on 64-bit,
but it did for 32-bit.

There is about 5 registers per channel with 0x4000 stride between them,
blame Apple (or Samsung? I don’t know...).

--
Martin