x86/UV2: Work around BAU bug

This patch implements a workaround for a UV2 hardware bug.
The bug is a non-atomic update of a memory-mapped register. When
hardware message delivery and software message acknowledge occur
simultaneously the pending message acknowledge for the arriving
message may be lost.  This causes the sender's message status to
stay busy.

Part of the workaround is to not acknowledge a completed message
until it is verified that no other message is actually using the
resource that is mistakenly recorded in the completed message.

Part of the workaround is to test for long elapsed time in such
a busy condition, then handle it by using a spare sending
descriptor. The stay-busy condition is eventually timed out by
hardware, and then the original sending descriptor can be
re-used. Most of that logic change is in keeping track of the
current descriptor and the state of the spares.

The occurrences of the workaround are added to the BAU
statistics.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Link: http://lkml.kernel.org/r/20120116211947.GC5767@sgi.com
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 1 deletions

diff --git a/arch/x86/include/asm/uv/uv_bau.h b/arch/x86/include/asm/uv/uv_bau.h
index 4a46b27ee9a0..1b82f7e87393 100644
--- a/arch/x86/include/asm/uv/uv_bau.h
+++ b/arch/x86/include/asm/uv/uv_bau.h
@@ -167,6 +167,7 @@
 #define FLUSH_RETRY_TIMEOUT             2
 #define FLUSH_GIVEUP                    3
 #define FLUSH_COMPLETE                  4
+#define FLUSH_RETRY_BUSYBUG             5
 
 /*
  * tuning the action when the numalink network is extremely delayed
@@ -463,7 +464,6 @@ struct bau_pq_entry {
 struct msg_desc {
         struct bau_pq_entry     *msg;
         int                     msg_slot;
-        int                     swack_slot;
         struct bau_pq_entry     *queue_first;
         struct bau_pq_entry     *queue_last;
 };
@@ -517,6 +517,9 @@ struct ptc_stats {
         unsigned long   s_retry_messages;       /* retry broadcasts */
         unsigned long   s_bau_reenabled;        /* for bau enable/disable */
         unsigned long   s_bau_disabled;         /* for bau enable/disable */
+        unsigned long   s_uv2_wars;             /* uv2 workaround, perm. busy */
+        unsigned long   s_uv2_wars_hw;          /* uv2 workaround, hiwater */
+        unsigned long   s_uv2_war_waits;        /* uv2 workaround, long waits */
         /* destination statistics */
         unsigned long   d_alltlb;               /* times all tlb's on this
                                                    cpu were flushed */
@@ -593,6 +596,8 @@ struct bau_control {
         short                   cpus_in_socket;
         short                   cpus_in_uvhub;
         short                   partition_base_pnode;
+        short                   using_desc; /* an index, like uvhub_cpu */
+        unsigned int            inuse_map;
         unsigned short          message_number;
         unsigned short          uvhub_quiesce;
         short                   socket_acknowledge_count[DEST_Q_SIZE];
@@ -610,6 +615,7 @@ struct bau_control {
         int                     cong_response_us;
         int                     cong_reps;
         int                     cong_period;
+        unsigned long           clocks_per_100_usec;
         cycles_t                period_time;
         long                    period_requests;
         struct hub_and_pnode    *thp;
@@ -670,6 +676,11 @@ static inline void write_mmr_sw_ack(unsigned long mr)
         uv_write_local_mmr(UVH_LB_BAU_INTD_SOFTWARE_ACKNOWLEDGE_ALIAS, mr);
 }
 
+static inline void write_gmmr_sw_ack(int pnode, unsigned long mr)
+{
+        write_gmmr(pnode, UVH_LB_BAU_INTD_SOFTWARE_ACKNOWLEDGE_ALIAS, mr);
+}
+
 static inline unsigned long read_mmr_sw_ack(void)
 {
         return read_lmmr(UVH_LB_BAU_INTD_SOFTWARE_ACKNOWLEDGE);