The Power Management Quality of Service (PM QoS) allows to
aggregate constraints from multiple entities. It is currently
used to manage the min/max frequency of a given policy.

Frequency constraints can come from:
- Thermal framework: acpi_thermal_cpufreq_init()
- Firmware: _PPC objects: acpi_processor_ppc_init()
- User: by setting policyX/scaling_[min|max]_freq
The minimum of the max frequency constraints is used to compute
the resulting maximum allowed frequency.

When enabling boost frequencies, the same frequency request object
(policy->max_freq_req) as to handle requests from users is used.
As a result, when setting:
- scaling_max_freq
- boost
The last sysfs file used overwrites the request from the other
sysfs file.

To avoid this:
1. Create a per-policy boost_freq_req to save the boost
constraints instead of overwriting the last scaling_max_freq
constraint.

2. policy_set_boost() calls the cpufreq set_boost callback.
Update the newly added boost_freq_req request from there:
- whenever boost is toggled
- to cover all possible paths

3. In the existing set_boost() callbacks:
- Don't update policy->max as this is done through the qos notifier
  cpufreq_notifier_max() which calls cpufreq_set_policy().
- Remove freq_qos_update_request() calls as the qos request is now
  done in policy_set_boost() and updates the new boost_freq_req

------------

E.g.:
On a Juno with available frequencies: 600.000, 1.000.000
Boost frequencies: 1.200.000
Using the cppc-cpufreq driver.

---
Without the patches:
# ## Init state
scaling_max_freq:1000000
cpuinfo_max_freq:1000000

# echo 700000 > scaling_max_freq
scaling_max_freq:700000
cpuinfo_max_freq:1000000

# echo 1 > ../boost
scaling_max_freq:1200000
cpuinfo_max_freq:1200000

# echo 800000 > scaling_max_freq
scaling_max_freq:800000
cpuinfo_max_freq:1200000

# echo 0 > ../boost
scaling_max_freq:1000000
cpuinfo_max_freq:1000000

---
With the patches:
# ## Init
scaling_max_freq:1000000
cpuinfo_max_freq:1000000

# echo 700000 > scaling_max_freq
scaling_max_freq:700000
cpuinfo_max_freq:1000000

# echo 1 > ../boost
scaling_max_freq:700000
cpuinfo_max_freq:1200000

# echo 800000 > scaling_max_freq
scaling_max_freq:800000
cpuinfo_max_freq:1200000

# echo 0 > ../boost
scaling_max_freq:800000
cpuinfo_max_freq:1000000

---

With the patches, the maximum scaling frequency requested is
conserved even though boosting is enabled/disabled.

The patches might be eligible for a stable tag.

Pierre Gondois (4):
  Revert "cpufreq: Fix re-boost issue after hotplugging a CPU"
  cpufreq: Add boost_freq_req QoS request
  cpufreq: Centralize boost freq QoS requests
  cpufreq: Update set_boost callbacks to rely on boost_freq_req

 drivers/cpufreq/amd-pstate.c   |  2 --
 drivers/cpufreq/cppc_cpufreq.c | 20 +++---------
 drivers/cpufreq/cpufreq.c      | 59 ++++++++++++++++++++++++++--------
 include/linux/cpufreq.h        |  1 +
 4 files changed, 50 insertions(+), 32 deletions(-)

--
2.43.0