powerpc/pseries: Limit PVR list to 16 entries for CAS negotiation

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Current Power system firmware caps the PVR list array size at 16 entries
during CAS (Client Architecture Support) negotiation. Passing more than
capped size to older firmware could cause an undefined behaviour and
breaks compatibility.

Future Power system firmware releases will lift this restriction and
support greater than 16 array entries.

Ensure that when running on Power11 or below hardware, the number
of PVR entries passed during CAS negotiation does not exceed the
firmware-imposed limit of 16.

In prom_send_capabilities(), compute start_index to skip the oldest
leading pvrs[] entries when running on Power11 or below hardware, so
that the pointer passed to ibm,client-architecture-support points to
ibm_architecture_vec.pvrs[start_index], presenting exactly 16 entries to
firmware.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Tested-by: Praveen K Pandey <praveen@linux.ibm.com>
Reviewed-by: Nikhil Kumar Singh <nikhilks@linux.ibm.com>
Reviewed-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260806051120.3703698-2-mahesh@linux.ibm.com

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Mahesh Salgaonkar 2026-08-06 10:41:17 +05:30 • committed by Madhavan Srinivasan

parent 5458b50b52

commit 972a7b7872

1 changed files with 28 additions and 6 deletions

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arch/powerpc/kernel/prom_init.c

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