[PATCH v4 1/4] powerpc/pseries: Limit PVR list to 16 entries for CAS negotiation

[Mahesh Salgaonkar <mahesh@linux.ibm.com>]

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>
---
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(-)

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 53503937de0e..055cb5f2d37f 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),
+		},
 		{
 			.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),
@@ -1403,6 +1409,22 @@ 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 +1449,7 @@ 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