On Wed, Sep 17, 2025 at 08:24:47AM -0700, Kevin Hilman wrote:

Michael Walle [off-list ref] writes:

quoted

The TISCI firmware will return 0 if the clock or consumer is not
enabled although there is a stored value in the firmware. IOW a call to
set rate will work but at get rate will always return 0 if the clock is
disabled.
The clk framework will try to cache the clock rate when it's requested
by a consumer. If the clock or consumer is not enabled at that point,
the cached value is 0, which is wrong.

Hmm, it also seems wrong to me that the clock framework would cache a
clock rate when it's disabled.  On platforms with clocks that may have
shared management (eg. TISCI or other platforms using SCMI) it's
entirely possible that when Linux has disabled a clock, some other
entity may have changed it.

It doesn't really help that the CCF doesn't seem to agree on if it
should do that in the first place :)

In the original clk API definition, you're not supposed to call
clk_get_rate() when the clock is disabled.

https://elixir.bootlin.com/linux/v6.16.8/source/include/linux/clk.h#L746

However, it's been allowed by the CCF since forever:

https://elixir.bootlin.com/linux/v6.16.8/source/drivers/clk/clk.c#L1986

But then, some drivers will return 0 as a valid value, and not an error
code (whatever 0Hz for a clock means).

It's kind of a mess, and very regression prone, so I don't really expect
it to change anytime soon.

Maxime