ACPI: CPPC: Serialize PCC EPP payload updates

cppc_set_epp_perf() stages Autonomous Selection and Energy Performance
Preference in the PCC shared region before taking pcc_lock. The platform
may still own the subspace, or a concurrent command may consume or
overwrite only part of the new payload.

Take the PCC write lock and wait for OSPM ownership before staging either
control. Keep the lock held until the complete payload has been submitted
with CMD_WRITE, so firmware cannot observe a mixed transaction.

For a mixed PCC/non-PCC description, complete every fallible non-PCC write
before staging PCC data. Cross-address-space updates cannot be atomic, but
a non-PCC failure can no longer leave an unsent value in shared memory for
a later PCC command to consume. Reject an unsupported PCC width before any
non-PCC control is changed.

Classify every writable control as either PCC or non-PCC. For SystemIO,
require port-I/O support and an access within the port range. Require
natural alignment on non-x86 platforms, whose port-I/O accessors use MMIO;
x86 port instructions support unaligned addresses. Also require a field
covering the complete access unit. cpc_write() performs a raw whole-port
write, so any other geometry could update the wrong bits or corrupt an
adjacent field.

If ownership acquisition or PCC staging fails, abort any older pending
performance batch before releasing the exclusive lock so its Phase-II
waiters receive the error instead of sleeping indefinitely.

This follows the PCC ownership sequence in ACPI 6.5 Section 14.5.

Fixes: 7bc1fcd39901 ("ACPI: CPPC: Add AMD pstate energy performance preference cppc control")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260724134251.1632824-1-christian.loehle%40arm.com
Link: https://sashiko.dev/#/patchset/20260807111303.1062391-1-christian.loehle%40arm.com
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Sumit Gupta <sumitg@nvidia.com>
Link: https://patch.msgid.link/20260916162805.1039247-6-christian.loehle@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

0 files changed, 0 insertions, 0 deletions