Re: [PATCH V5 1/2] cpufreq: add support for intermediate (stable) frequencies

[Doug Anderson]

Viresh,

On Mon, Jun 2, 2014 at 10:19 AM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> Douglas Anderson, recently pointed out an interesting problem due to which
> udelay() was expiring earlier than it should.
>
> While transitioning between frequencies few platforms may temporarily switch to
> a stable frequency, waiting for the main PLL to stabilize.
>
> For example: When we transition between very low frequencies on exynos, like
> between 200MHz and 300MHz, we may temporarily switch to a PLL running at 800MHz.
> No CPUFREQ notification is sent for that. That means there's a period of time
> when we're running at 800MHz but loops_per_jiffy is calibrated at between 200MHz
> and 300MHz. And so udelay behaves badly.
>
> To get this fixed in a generic way, lets introduce another set of callbacks
> get_intermediate() and target_intermediate(), only for drivers with
> target_index() and CPUFREQ_ASYNC_NOTIFICATION unset.
>
> get_intermediate() should return a stable intermediate frequency platform wants
> to switch to, and target_intermediate() should set CPU to to that frequency,
> before jumping to the frequency corresponding to 'index'. Core will take care of
> sending notifications and driver doesn't have to handle them in
> target_intermediate() or target_index().
>
> NOTE: ->target_index() should restore to policy->restore_freq in case of
> failures as core would send notifications for that.
>
> Tested-by: Stephen Warren <swarren@xxxxxxxxxx>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
>  Documentation/cpu-freq/cpu-drivers.txt | 29 ++++++++++++++-
>  drivers/cpufreq/cpufreq.c              | 67 ++++++++++++++++++++++++++++++----
>  include/linux/cpufreq.h                | 25 +++++++++++++
>  3 files changed, 112 insertions(+), 9 deletions(-)

LGTM.  Thanks for doing this!  :)

Reviewed-by: Doug Anderson <dianders@xxxxxxxxxxxx>
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