Re: [PATCH v2 0/2] cpufreq/amd-pstate: Fix EPP initialization and add capability check

[Mario Limonciello]

On 6/3/26 06:56, Marco Scardovi wrote:
> Hi Prateek and all,
>
> before trying merging in @Mario's git il post the new patches with the
> changes you suggested. If something doesn't feel right let me know.
>
> This series addresses a boot-time performance regression on shared memory
> systems where the CPU gets stuck at the lowest non-linear frequency
> (1.7GHz), and adds proper EPP capability checks to prevent active mode from
> being incorrectly enabled on systems without EPP support.
>
> Patch 1 fixes the boot-time initialization regression by introducing an
> `epp_hw_programmed` flag in struct amd_cpudata to track whether EPP has
> been configured on the hardware. This bypasses a false cache hit on boot
> due to zero-initialized caching registers, ensuring that EPP and auto_sel
> are always written during CPU initialization, while still preserving the
> cache guard optimization for all subsequent runtime transitions.
>
> Patch 2 implements an EPP capability check at boot time using a new
> amd_pstate_epp_supported() helper, which queries the EPP performance
> capability on the first online CPU. If EPP is unsupported, the driver falls
> back to passive mode at boot, and rejects any subsequent runtime
> transitions to active mode.
>
> Changes in v2:
> - Patch 1: Rename `epp_initialized` to `epp_hw_programmed`, explicitly
>    document the flag semantics, and add a comment documenting the EPP cache
>    guard optimization behavior.
> - Patch 2: Add comments explaining the uniform CPU capability check on x86,
>    handle EPP capability check errors robustly using a tri-state model (only
>    treat -EOPNOTSUPP as unsupported, warn and assume supported for other
>    errors to avoid false negatives), and reject runtime active mode transitions
>    at sysfs store time (preventing the driver from being left in an
>    unregistered state).
>
> Changes in v1:
> - Fix the boot-time CPPC EPP/auto_sel initialization regression in
>    shmem_set_epp() using a state tracking flag while preserving runtime
>    cache optimization.
> - Add an EPP capability check helper during initialization.
> - Fall back to passive mode at boot if EPP is not supported, and reject
>    transitions to active mode at runtime if EPP is not supported.
>
> Marco Scardovi (2):
>    cpufreq/amd-pstate: Fix EPP initialization for shared memory systems
>    cpufreq/amd-pstate: Prevent active mode on systems without EPP support
>
>   drivers/cpufreq/amd-pstate.c | 52 +++++++++++++++++++++++++++++++++++-
>   drivers/cpufreq/amd-pstate.h |  2 ++
>   2 files changed, 53 insertions(+), 1 deletion(-)

Did you see Prateek's suggestion?  Can you check if that helps before we 
go down this path?

Thanks,