[tip:x86/platform] x86/platform/uv/BAU: Fix payload queue setup on UV4 hardware

[tip-bot for Andrew Banman <tipbot@zytor.com>]

Commit-ID:  6d78059bbc0ace5461938aaea8cda95eb6719898
Gitweb:     http://git.kernel.org/tip/6d78059bbc0ace5461938aaea8cda95eb6719898
Author:     Andrew Banman <abanman@sgi.com>
AuthorDate: Wed, 21 Sep 2016 11:09:20 -0500
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 22 Sep 2016 11:16:15 +0200

x86/platform/uv/BAU: Fix payload queue setup on UV4 hardware

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: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mike Travis <travis@sgi.com>
Acked-by: Dimitri Sivanich <sivanich@sgi.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: akpm@linux-foundation.org
Cc: rja@sgi.com
Link: http://lkml.kernel.org/r/1474474161-265604-10-git-send-email-abanman@sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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);