[PATCH v5 4/5] clk: add CLK_SET_RATE_NO_REPARENT flag

Hi Sylwester

On 25/07/13 13:34, Sylwester Nawrocki wrote:

On 06/13/2013 06:06 PM, James Hogan wrote:

quoted

Add a CLK_SET_RATE_NO_REPARENT clock flag, which will prevent muxes
being reparented during clk_set_rate.

To avoid breaking existing platforms, all callers of clk_register_mux()
are adjusted to pass the new flag. Platform maintainers are encouraged
to remove the flag if they wish to allow mux reparenting on set_rate.

[..]

quoted

Changes in v3:

* rename/invert CLK_SET_RATE_REMUX to CLK_SET_RATE_NO_REPARENT and move
  to this new patch.
* patch 3: add CLK_SET_RATE_NO_REPARENT flag to all callers of
  clk_register_mux. If you don't mind your clocks being reparented in
  response to set_rate please let me know and I'll drop the relevant
  portion of the patch.

Why is this better to change current behaviour of the clock core
and modify all drivers instead of having, e.g. CLK_SET_RATE_REPARENT
set in drivers of hardware that supports clock re-parenting while
setting clock rate ?

See this message from Mike Turquette which first suggested it:

http://marc.info/?l=linux-kernel&m=136847508109344&w=2

Is there intention to just have the automatic clock re-parenting
as a default feature in the common clock API ?

Yes, that would be the result (except where explicitly disallowed).
Unfortunately where such policy should ideally be defined is still up in
the air.

It's not a property of the hardware, but then it is arguably a property
of the environment the bootloader has configured (like the stuff in the
/chosen device tree node).

Presuming that the usual reason not to reparent a mux is because other
important clocks depend on it, the kernel might know enough to work out
whether it's safe (unless of course there are other cores/threads in the
SoC using the clock that Linux isn't aware of, which brings us back to
it being a bootloader environment thing).

My apologies if this has already been answered, I haven't been
following this thread.

No problem :)

Cheers
James