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Subject[PATCH v8 00/18] More improvements for Tegra30 devfreq driver
Date
Hello,

This series addresses some additional review comments that were made by
Thierry Reding to [1], makes several important changes to the driver,
reducing interrupts activity, and adds new features. In the end I'm
proposing myself as a maintainer for the Tegra devfreq drivers.

[1] https://lore.kernel.org/lkml/0fb50eb1-a173-1756-6889-2526a10ac707@gmail.com/T/

Changelog:

v8: Addressed review comments that were made by Chanwoo Choi to v7 by:

1. Taking into account suggestions that were made for the "Add new
interrupt_driven flag for governors".

2. Patch "Support variable polling interval" now doesn't use
devfreq->stop_polling and uses tegra->cur_freq instead. There is
now a comment for the 256ms max polling interval limitation as well.

The patch "Increase sampling period to 16ms" is dropped from the series
for now since we found out that it doesn't bring much benefit.

The cur_freq value is now refreshed after clk-notifier registration in
the "Move clk-notifier's registration to governor's start" patch, for
consistency. This also becomes useful for the "Support variable polling
interval" patch since it now uses the cur_freq for tracking of the
governor's enable-state.

The patch "Support variable polling interval" now has a proper scaling
of the dependency threshold value, which I missed to backport into
v7 after dropping some of the v6 patches. The do_percent() function
now doesn't suffer from integer overflow bug when freq, boosting and
polling interval values are too large.

v7: Addressed review comments that were made by Chanwoo Choi to v6 by:

1. Dropping patch "Ensure that target freq won't overflow".
2. Making "Use kHz units uniformly in the code" patch more easier
for review and improving its commit's message.
3. The "Support variable polling interval" patch is reworked, now it
doesn't touch things that should stay internal to devfreq core, like
devfreq->stop_polling and etc. In a result a new generic
interrupt_driven flag is available for devfreq governors (added in a
new patch "Add new interrupt_driven flag for governors").

Patch "Set up watermarks properly" and related to it patches are dropped
because I found a case where it doesn't work well. These patches need
some more thought and not ready for now, I'll continue working on them.
I extracted useful changes from the dropped patches and then tuned up
MCCPU boost-down coefficient to keep ACTMON silent when system is idling,
in a result there are these new patches:

1. Don't enable already enabled consecutive interrupts
2. Disable consecutive interrupts when appropriate
3. Tune up MCCPU boost-down coefficient

v6: Addressed review comment that was made by Chanwoo Choi to v5 by
squashing "Define ACTMON_DEV_CTRL_STOP" patch into the "Use CPUFreq
notifier" patch.

v5: Addressed review comments that were made by Chanwoo Choi to v4 by
squashing few patches, dropping some questionable patches, rewording
comments to the code, restructuring the code and etc.

These patches are now dropped from the series:

PM / devfreq: tegra30: Use tracepoints for debugging
PM / devfreq: tegra30: Inline all one-line functions

The interrupt-optimization patches are squashed into a single patch:

PM / devfreq: tegra30: Reduce unnecessary interrupts activity

because it's better to keep the optimizations as a separate change and
this also helps to reduce code churning, since the code changes depend
on a previous patch in order to stay cleaner.

Fixed a lockup bug that I spotted recently, which is caused by a
clk-notifier->cpufreq_get()->clk_set_rate() sequence. Now a non-blocking
variant of CPU's frequency retrieving is used, i.e. cpufreq_quick_get().

Further optimized the CPUFreq notifier by postponing the delayed
updating in accordance to the polling interval, this actually uncovered
the above lockup bug.

Implemented new minor driver feature in the new patch:

PM / devfreq: tegra30: Support variable polling interval

v4: Added two new patches to the series:

PM / devfreq: tegra30: Synchronize average count on target's update
PM / devfreq: tegra30: Increase sampling period to 16ms

The first patch addresses problem where governor could get stuck due
to outdated "average count" value which is snapshoted by ISR and there
are cases where manual update of the value is required.

The second patch is just a minor optimization.

v3: Added support for tracepoints, replacing the debug messages.
Fixed few more bugs with the help of tracepoints.

New patches in this version:

PM / devfreq: tegra30: Use tracepoints for debugging
PM / devfreq: tegra30: Optimize CPUFreq notifier
PM / devfreq: tegra30: Optimize upper consecutive watermark selection
PM / devfreq: tegra30: Optimize upper average watermark selection
PM / devfreq: tegra30: Include appropriate header

Some of older patches of this series also got some extra minor polish.

v2: Added more patches that are cleaning driver's code further and
squashing another kHz conversion bug.

The patch "Rework frequency management logic" of the v1 series is now
converted to "Set up watermarks properly" because I found some problems
in the original patch and then realized that there is no need to change
the logic much. So the logic mostly preserved and only got improvements.

The series is based on the today's linux-next (25 Jun) and takes into
account minor changes that MyungJoo Ham made to the already queued
patches from the first batch [1].

Dmitry Osipenko (18):
PM / devfreq: tegra30: Change irq type to unsigned int
PM / devfreq: tegra30: Keep interrupt disabled while governor is
stopped
PM / devfreq: tegra30: Handle possible round-rate error
PM / devfreq: tegra30: Drop write-barrier
PM / devfreq: tegra30: Fix integer overflow on CPU's freq max out
PM / devfreq: tegra30: Use kHz units uniformly in the code
PM / devfreq: tegra30: Use CPUFreq notifier
PM / devfreq: tegra30: Move clk-notifier's registration to governor's
start
PM / devfreq: tegra30: Reset boosting on startup
PM / devfreq: tegra30: Don't enable consecutive-down interrupt on
startup
PM / devfreq: tegra30: Constify structs
PM / devfreq: tegra30: Include appropriate header
PM / devfreq: tegra30: Don't enable already enabled consecutive
interrupts
PM / devfreq: tegra30: Disable consecutive interrupts when appropriate
PM / devfreq: Add new interrupt_driven flag for governors
PM / devfreq: tegra30: Support variable polling interval
PM / devfreq: tegra30: Tune up MCCPU boost-down coefficient
PM / devfreq: tegra20/30: Add Dmitry as a maintainer

MAINTAINERS | 9 +
drivers/devfreq/devfreq.c | 9 +-
drivers/devfreq/governor.h | 3 +
drivers/devfreq/tegra30-devfreq.c | 394 +++++++++++++++++++++---------
4 files changed, 303 insertions(+), 112 deletions(-)

--
2.23.0

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