Re: Informing common clock framework driver of externally-derived base clock frequency

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

Hi,

Cc: CCF maintainers

On 1/4/19 03:35, Jonny Hall wrote:
[...]

> ... However, in my application, the input frequency of
> the si5342 is not known in advance, is derived from an external
> source, and can change during runtime. The si5342 will need to be
> (re)configured during operation with the frequency of this root clock
> source in order to properly lock onto it and generate the correct
> output frequencies -- it cannot independently determine the input
> frequency, only "locked" / "unlocked" state.  The application software
> (other drivers and usermode application code) will know the input
> clock rate.  I've though of a couple ways to do this:
> 
> -Implement the root clock source as an "imaginary" divider where the
> set_rate call actually configures the input dividers of the si5342.
> This approach seems to abuse the common clock framework, as I'm not
> actually *setting* the rate, I'm *informing* the driver of a rate that
> was determined independently.

It sounds like registering a clk notifier on the si5342 root source clock
might be a way to go, wouldn't that work for you?
For an example you could have a look at drivers/clk/sunxi-ng/ccu_mux.c.

--
Regards,
Sylwester