[PATCH V4 0/3] cpufreq: add support for intermediate (stable) frequencies

Viresh Kumar
2014-05-21T09:04:34Z

Doug raised many important concerns on V3:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg645134.html

and so here is another iteration with improvements.

@Stephen: I have dropped you Tested-by's as patches are updated and requires a
retest, sorry for that :(

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().

This patchset also update Tegra to use this new infrastructure and is already
tested by Stephen.

V3->V4:
- Allow get_intermediate() to return zero when we don't need to switch to
intermediate first
- Get rid of 'goto' and create another routine for handling intermediate freqs
- Allow target_index() to fail, its not a crime :)
- Fix tegra driver to return zero from get_intermediate() for few situations
(refer to patch 3/4)
- Fix issues with tegra's patch, like s/rate/rate * 1000
- Overall there are more modifications that what Doug requested as I felt we
need better support from core.
- Looks much better now, thanks Doug :)

V2-V3:
- Fix spelling error: s/Uset/Used
- Update tegra with the changes Stephen suggested
- Include a dependency patch sent separately earlier (3/4)

V1-V2: Almost changed completely, V1 was here: https://lkml.org/lkml/2014/5/15/40

Viresh Kumar (3):
cpufreq: handle calls to ->target_index() in separate routine
cpufreq: add support for intermediate (stable) frequencies
cpufreq: Tegra: implement intermediate frequency callbacks

Documentation/cpu-freq/cpu-drivers.txt | 29 ++++++++-
drivers/cpufreq/cpufreq.c | 111 ++++++++++++++++++++++++++-------
drivers/cpufreq/tegra-cpufreq.c | 81 ++++++++++++++----------
include/linux/cpufreq.h | 25 ++++++++
4 files changed, 186 insertions(+), 60 deletions(-)

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2.0.0.rc2