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The values written to these registers can > be lost: > > - Across CPU hotplug or suspend/resume: the platform may reset them > while the CPU is offline. > - On driver unload: the driver-written value is left in the register > instead of returning to its pre-driver state. > > Handle these with: > > - Patch 1: adds online()/offline() callbacks so the core keeps policy > alive across CPU hotplug instead of tearing it down and rebuilding it. > - Patch 2: makes the autonomous selection register helpers take a u64. > - Patch 3: adds a table-driven mechanism that captures each register's > firmware value at init(), restores it from offline(), and reapplies > the OSPM-set value from online(). > - Patch 4: extends the same save/restore to system suspend/resume. Gentle reminder. Could this be considered for queuing if nothing further needs addressing. Thanks, Sumit > v3[3] -> v4: > - Patch 1: > - offline() parks the perf request at lowest_perf, as exit() did. > - online() resyncs the frequency invariance counters. > - raise MAX before the perf restore when the saved MIN is above it. > - Patch 3: > - write auto_sel first when enabling it and last when disabling it. > - replace the four save/restore helpers into save_regs() and > apply_saved_regs(), each taking the firmware or requested type. > - keep the per-policy saved values in one struct, and name each > register for the pr_debug diagnostics. > - Patch 4: > - suspend() also restores the firmware values and flags it, so > offline() skips them and resume() only handles still-online policies. > > Sumit Gupta (4): > cpufreq: CPPC: Keep the policy across CPU hotplug > ACPI: CPPC: Make autonomous selection helpers take a u64 > cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload > cpufreq: CPPC: Preserve OSPM-set registers across suspend/resume > > drivers/acpi/cppc_acpi.c | 20 +- > drivers/cpufreq/amd-pstate.c | 2 +- > drivers/cpufreq/cppc_cpufreq.c | 369 ++++++++++++++++++++++++++++++++- > include/acpi/cppc_acpi.h | 8 +- > 4 files changed, 376 insertions(+), 23 deletions(-) > > [1] v1: https://lore.kernel.org/lkml/20260623095403.3407436-1-sumitg@nvidia.com/ > [2] v2: https://lore.kernel.org/lkml/20260716153820.2007095-1-sumitg@nvidia.com/ > [3] v3: https://lore.kernel.org/lkml/20260724215937.3368276-1-sumitg@nvidia.com/ >