[RFC Patch v2 0/3] add temporary parent migration support
Tomasz Figa
tomasz.figa at gmail.com
Tue Sep 3 18:36:50 EDT 2013
Hi Chander,
On Tuesday 03 of September 2013 17:04:28 Chander Kashyap wrote:
> Some platform has provision to change cpu parent clock during
> cpu frequency scaling. This patch series provides a mechanism to
> implement the same using CCF.
>
> Patch1 provides mechanism to migrate to new parent temporarily.
>
> Patch2 updates the user of clk_register_mux and DEFINE_CLK_MUX which are
> modified to add support for clk migration.
>
> Patch3 adds support to Exynos5250 to use the clock parent migration
> feature implemented in CCF.
I don't really like this approach. A need to change mux setting
temporarily is heavily platform-specific and I don't think it should be
handled by generic code. First of all there are many factor that you would
have to account for to make this solution generic, such as:
- board specific alternative parents,
- exact moment of parent change,
- some other platform specific conditions, like CPU voltage that must be
changed when mux is changed, because it changes CPU frequency,
- and probably a lot of more factors that only people working with all
the platforms supported (and unsupported yet) by Linux.
I can see at least two solutions for this problem that don't require
changing core code of common clock framework:
1) Implementing a special clock type using normal mux ops, but also
registering a notifier for its PRE_RATE_CHANGE and POST_RATE_CHANGE events
to perform parent switching.
2) Using normal mux clock, but registering such notifiers in clock
controller or cpufreq driver.
Best regards,
Tomasz
More information about the linux-arm-kernel
mailing list