On 2026/08/03 09:27 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 <[email protected]>
> Tested-by: Praveen K Pandey <[email protected]>
> ---
> Change in v2:
> - Define a named macro CAS_MAX_PVR_ENTRIES
> ---
> arch/powerpc/kernel/prom_init.c | 35 ++++++++++++++++++++++++++-------
> 1 file changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index 53503937de0ee..6b50870759fd9 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -86,6 +86,12 @@
> */
> #define ADDR(x) (u32)(unsigned long)(x)
>
> +/*
> + * Current Power system firmware caps the PVR list array size at 16 entries
> + * during CAS (Client Architecture Support) negotiation.
> + */
> +#define CAS_MAX_PVR_ENTRIES 16
> +
> #ifdef CONFIG_PPC64
> #define OF_WORKAROUNDS 0
> #else
> @@ -979,6 +985,10 @@ static const struct ibm_arch_vec
> ibm_architecture_vec_template __initconst = {
> .mask = cpu_to_be32(0xfffe0000), /* POWER5/POWER5+ */
> .val = cpu_to_be32(0x003a0000),
> },
> + {
> + .mask = cpu_to_be32(0xffffffff), /* all 2.04-compliant
> and earlier */
> + .val = cpu_to_be32(0x0f000001),
> + },
It may be a good idea to add a comment (like below) above .pvrs = {
explaining why the oldest entries are at the front, otherwise the intent
of start_index trimming from the front is not obvious to future
contributors:
/*
* The oldest/least-capable entries are placed at the FRONT so that
* start_index trims them first when running on older firmware (Power11
* and below) that caps the array at CAS_MAX_PVR_ENTRIES entries. As
* newer processors are added, more old front entries will naturally
* fall outside the firmware window. New entries must be inserted in
* newest-first order AFTER these oldest front entries.
*/
> {
> .mask = cpu_to_be32(0xffff0000), /* POWER6 */
> .val = cpu_to_be32(0x003e0000),
> @@ -1032,13 +1042,9 @@ static const struct ibm_arch_vec
> ibm_architecture_vec_template __initconst = {
> .val = cpu_to_be32(0x0f000003),
> },
> {
> - .mask = cpu_to_be32(0xffffffff), /* all 2.05-compliant
> */
> + .mask = cpu_to_be32(0xfffffffd), /* all 2.05-compliant
> */
> .val = cpu_to_be32(0x0f000002),
> },
> - {
> - .mask = cpu_to_be32(0xfffffffe), /* all 2.04-compliant
> and earlier */
> - .val = cpu_to_be32(0x0f000001),
> - },
> },
>
> .num_vectors = NUM_VECTORS(6),
> @@ -1347,7 +1353,6 @@ static void __init prom_check_platform_support(void)
> };
> int prop_len = prom_getproplen(prom.chosen,
> "ibm,arch-vec-5-platform-support");
> -
Nit: Looks unintentional whitespace change, please drop.
> /*
> * First copy the architecture vec template
> *
> @@ -1403,6 +1408,22 @@ static void __init prom_send_capabilities(void)
> ihandle root;
> prom_arg_t ret;
> u32 cores;
> + int start_index = 0;
> +
> + /*
> + * 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.
> + *
> + * Compute the 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.
> + */
> + if ((ARRAY_SIZE(ibm_architecture_vec_template.pvrs) >
> CAS_MAX_PVR_ENTRIES) &&
> + (PVR_VER(mfspr(SPRN_PVR)) <= PVR_POWER11))
> + start_index = ARRAY_SIZE(ibm_architecture_vec_template.pvrs) -
> CAS_MAX_PVR_ENTRIES;
>
> /* Check ibm,arch-vec-5-platform-support and fixup vec5 if required */
> prom_check_platform_support();
> @@ -1427,7 +1448,7 @@ static void __init prom_send_capabilities(void)
> if (call_prom_ret("call-method", 3, 2, &ret,
> ADDR("ibm,client-architecture-support"),
> root,
> - ADDR(&ibm_architecture_vec)) == 0) {
> +
> ADDR(&ibm_architecture_vec.pvrs[start_index])) == 0) {
> /* the call exists... */
> if (ret)
> prom_printf("\nWARNING: ibm,client-architecture"
> --
> 2.55.0
>
>
