On 4/13/23 02:39, Krzysztof Kozlowski wrote:
On 13/04/2023 00:24, Brenda Streiff wrote:
On 4/11/23 00:44, Krzysztof Kozlowski wrote:
On 10/04/2023 23:11, Brenda Streiff wrote:
+
+ interrupts:
+ maxItems: 1
+
+ clock-frequency: true
I missed it last time - why do you need this property? You do not have
any clock input, so which clock's frequency is it?
This is the clock frequency of the UART; on our x86-based platforms this
comes from the LPC clock, on Zynq-7000 it's derived from a clock in the
FPGA. This is used to set struct uart_port::uartclk in the serial core,
as it is for other UARTs.
This clock frequency can vary based on board design (especially on the
x86 side, due to different LPC clocks) but for a given design is fixed-
frequency.
So you must have clock input - clocks property. Once you add this, use
assigned-clocks to get the rate you want.
Would you prefer this be documented further? I was following 8250.yaml's
lead here with the simple `true`.
I prefer to drop it. It is not correct and a legacy property. Without
clock inputs how can you even configure some clock?
Configure in what respect? Software can't change this clock; it's
effectively a fixed oscillator.
In practice, this would always be pointing at a compatible="fixed-clock"
which declares a clock-frequency; this seems like "clock-frequency but
more steps". I can add that, but I'm not clear on what value that adds.
We also have shipping devices with ACPI tables using "clock-frequency",
so independent of support for "clocks" and "assigned-clocks" for
devicetree-using systems, I would still have to keep support in the
driver for a "clock-frequency" device property for ACPI-using systems.
(Is there documentation on a standalone clock-property being a legacy
property that I've missed? I don't see anything of the sort in
writing-bindings.rst or in dt-schema and I want to make sure that I
haven't missed the proper guidance here.)
