Re: [PATCH v3 1/4] powerpc/pseries: Limit PVR list to 16 entries for CAS negotiation

[Amit Machhiwal <amachhiw@linux.ibm.com>]

On 2026/08/05 04:39 PM, Mahesh Salgaonkar wrote:
> 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>
> ---
> Change in v3:
> - Remove unintentional whitespace change.
> 
> Change in v2:
> - Define a named macro CAS_MAX_PVR_ENTRIES
> ---
>  arch/powerpc/kernel/prom_init.c | 34 +++++++++++++++++++++++++++------
>  1 file changed, 28 insertions(+), 6 deletions(-)

Reviewed-by: Amit Machhiwal <amachhiw@linux.ibm.com>

~Amit