Re: [PATCH 2/3] mailbox: pcc: Check shared memory signature on request

On 7/17/2026 3:56 PM, Sudeep Holla wrote:
> ACPI 6.6 Tables 14.9 and 14.12 define the PCC shared memory
> signature as the bitwise OR of 0x50434300 and the PCC subspace ID.
> They also clarify that the signature is populated by the platform and
> verified by OSPM. The signature is at byte offset 0 in the generic,
> extended and reduced PCC shared memory layouts.
>
> Check the signature when a client requests a PCC mailbox channel,
> after mapping shared memory and before binding the mailbox client.
> This keeps the check in the PCC mailbox controller instead of
> duplicating it in individual clients.
>
> Treat a signature mismatch as a warning rather than rejecting the
> channel request. Making this newly added check fatal could break
> existing systems whose firmware did not populate the signature
> correctly even though PCC communication works. Continue to reject
> shared memory that is too small to contain a signature because it
> cannot be inspected safely.
>
> Cc: Jassi Brar <[email protected]>
> Cc: Huisong Li <[email protected]>
> Signed-off-by: Sudeep Holla <[email protected]>
> ---
LGTM,
Acked-by: Huisong Li <[email protected]>