19.08.2021 19:31, Thierry Reding пишет:

quoted

The "device" representation is internal to the kernel. It's okay to me
to have PLLs represented by a device, it's a distinct h/w by itself.

CCF supports managing of clock's RPM and it requires to have clock to be
backed by a device. That's what we are using here.

Please see
https://elixir.bootlin.com/linux/v5.14-rc6/source/drivers/clk/clk.c#L109

Looking at the implementation of __clk_register() and where that device
pointer typically comes from, I don't think the way this is used here is
what was intended. The way I interpret the code is that a clock is
registered with a parent device (i.e. its provider) and
clk_pm_runtime_get() is then used internally as a way to make sure that
when a clock is prepared, it's parent device is runtime resumed. This is
presumably to ensure that any registers that the driver might need to
access in order to prepare and enable the clock are accessible (i.e. the
CAR is not powered off or in reset).

So the struct device that is passed to __clk_register() (or its callers)
should be that of the CAR rather than virtual struct devices created by
the CAR.

And it's a bit debatable whether or not PLLs represent distinct
hardware. Ultimately every transistor on a chip could be considered
distinct hardware. But a platform device is a device on a platform bus,
which is really just another way of saying it's a hardware block that's
accessible from the CPU via a memory-mapped address. A PLL (just like
other clocks) is merely a resource exposed by means of access to these
registers. So I don't think they should be platform devices. Even making
them struct device:s seems a bit of a stretch.

Is there any reason why struct clk can't be used for this? I mean, the
whole purpose of that structure is to represent clocks. Why do we need
to make them special?

Because we need to perform DVFS for PLLs. The only way to do it without
having to reinvent existing frameworks is to use these frameworks and
they require a device.