[PATCH 09/10] arch/x86/platform/uv: BAU UV4 fix payload queue setup

[Andrew Banman <abanman@sgi.com>]

The BAU on UV4 does not need to maintain the payload queue tail pointer. Do
not initialize the tail pointer MMR on UV4.

Note that write_payload_tail is not an abstracted BAU function since it is
an operation specific to pre-UV4 versions. Then we must switch on the UV
version to control its usage, for which we use uvhub_version rather than
is_uv*_hub because it is quicker/more concise.

Signed-off-by: Andrew Banman <abanman@sgi.com>
Acked-by: Mike Travis <travis@sgi.com>
Acked-by: Dimitri Sivanich <sivanich@sgi.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/platform/uv/tlb_uv.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
index 72a5de7..7ca0e5c 100644
--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -1826,11 +1826,19 @@ static void pq_init(int node, int pnode)
 
 	first = ops.bau_gpa_to_offset(uv_gpa(pqp));
 	last = ops.bau_gpa_to_offset(uv_gpa(pqp + (DEST_Q_SIZE - 1)));
-	tail = first;
-	gnode = uv_gpa_to_gnode(uv_gpa(pqp));
-	first = (gnode << UV_PAYLOADQ_GNODE_SHIFT) | tail;
 
-	write_mmr_payload_tail(pnode, tail);
+	/*
+	 * Pre UV4, the gnode is required to locate the payload queue
+	 * and the payload queue tail must be maintained by the kernel.
+	 */
+	bcp = &per_cpu(bau_control, smp_processor_id());
+	if (bcp->uvhub_version <= 3) {
+		tail = first;
+		gnode = uv_gpa_to_gnode(uv_gpa(pqp));
+		first = (gnode << UV_PAYLOADQ_GNODE_SHIFT) | tail;
+		write_mmr_payload_tail(pnode, tail);
+	}
+
 	ops.write_payload_first(pnode, first);
 	ops.write_payload_last(pnode, last);
 	ops.write_g_sw_ack(pnode, 0xffffUL);
-- 
1.8.5.6