Messages in this thread | | | Date | Thu, 5 Jun 2014 12:51:30 -0700 | Subject | Re: [PATCH V5 1/2] cpufreq: add support for intermediate (stable) frequencies | From | Doug Anderson <> |
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Viresh,
On Mon, Jun 2, 2014 at 10:19 AM, Viresh Kumar <viresh.kumar@linaro.org> 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@nvidia.com> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > --- > 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@chromium.org>
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