ACPI: PCC: Preserve shared memory signature in OpRegion handler

ACPI 6.3 introduced PCC OperationRegions. Section 5.5.2.4.7.3,
"Declaring message fields within a PCC OperationRegion", states that,
for all PCC subspace types, the PCC Operation Region pertains to the
region of PCC subspace that succeeds the PCC signature. Its length
therefore excludes the 4-byte signature.

The PCC address space handler currently copies the OperationRegion
buffer to and from the start of the shared memory. This overwrites or
exposes the platform-populated signature and omits the final four bytes
of the OperationRegion.

Offset the copies by the size of the signature and reject an
OperationRegion that does not fit in the remaining shared memory.

The example added by commit 77e2a04745ff ("ACPI: PCC: Implement
OperationRegion handler for the PCC Type 3 subtype") incorrectly
included the signature as an OperationRegion field. A Type 3
OperationRegion containing a 100-byte communication area is declared
as follows:

OperationRegion (PFRM, PCC, 2, 0x70)
Field (PFRM, ByteAcc, NoLock, Preserve)
{
    FLGS,   32,
    LEN,    32,
    CMD,    32,
    DATA,   800
}

This contains three 32-bit fields followed by a 100-byte DATA field.
The fields correspond to the Type 3 shared memory layout in ACPI 6.3,
Table 14-372, after excluding its 4-byte signature.

Fixes: 77e2a04745ff ("ACPI: PCC: Implement OperationRegion handler for the PCC Type 3 subtype")
Reviewed-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>
Link: https://patch.msgid.link/20260922144302.3847593-3-sudeep.holla@kernel.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

0 files changed, 0 insertions, 0 deletions