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`amd_pstate_set_epp` function uses `cppc_req_cached` and `epp` variable to update the MSR_AMD_CPPC_REQ register for AMD MSR systems. The recent commit7cca9a9851("cpufreq: amd-pstate: avoid uninitialized variable use") changed the sequence of updating cppc_req_cached and writing the MSR_AMD_CPPC_REQ. Therefore while switching from powersave to performance governor and vice-versa in active mode MSR_AMD_CPPC_REQ is set with the previous cached value. To fix this: first update the `cppc_req_cached` variable and then call `amd_pstate_set_epp` function. - Before commit7cca9a9851("cpufreq: amd-pstate: avoid uninitialized variable use"): With powersave governor: [ 1.652743] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff [ 1.652744] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff [ 1.652746] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0 Changing to performance governor: [ 300.493842] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff [ 300.493846] amd_pstate_set_epp: writing cppc_req_cached = 0xffff [ 300.493847] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0 - After commit7cca9a9851("cpufreq: amd-pstate: avoid uninitialized variable use"): With powersave governor: [ 1.646037] amd_pstate_set_epp: writing cppc_req_cached = 0xffff [ 1.646038] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0 [ 1.646042] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff Changing to performance governor: [ 687.117401] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff [ 687.117405] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0 [ 687.117419] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff - After this fix: With powersave governor: [ 2.525717] amd_pstate_epp_init: writing to cppc_req_cached = 0x1eff [ 2.525720] amd_pstate_set_epp: writing cppc_req_cached = 0x1eff [ 2.525722] amd_pstate_set_epp: writing min_perf = 30, des_perf = 0, max_perf = 255, epp = 0 Changing to performance governor: [ 3440.152468] amd_pstate_epp_init: writing to cppc_req_cached = 0xffff [ 3440.152473] amd_pstate_set_epp: writing cppc_req_cached = 0xffff [ 3440.152474] amd_pstate_set_epp: writing min_perf = 255, des_perf = 0, max_perf = 255, epp = 0 Fixes:7cca9a9851("cpufreq: amd-pstate: avoid uninitialized variable use") Signed-off-by: Wyes Karny <wyes.karny@amd.com> Acked-by: Huang Rui <ray.huang@amd.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.