[MIPS] Workaround for RM7000 WAIT instruction aka erratum 38

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 25 insertions, 1 deletions

diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index c6b8b074a81a..06448a9656dc 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -75,6 +75,27 @@ static void r4k_wait_irqoff(void)
         local_irq_enable();
 }
 
+/*
+ * The RM7000 variant has to handle erratum 38.  The workaround is to not
+ * have any pending stores when the WAIT instruction is executed.
+ */
+static void rm7k_wait_irqoff(void)
+{
+        local_irq_disable();
+        if (!need_resched())
+                __asm__(
+                "       .set    push                                    \n"
+                "       .set    mips3                                   \n"
+                "       .set    noat                                    \n"
+                "       mfc0    $1, $12                                 \n"
+                "       sync                                            \n"
+                "       mtc0    $1, $12         # stalls until W stage  \n"
+                "       wait                                            \n"
+                "       mtc0    $1, $12         # stalls until W stage  \n"
+                "       .set    pop                                     \n");
+        local_irq_enable();
+}
+
 /* The Au1xxx wait is available only if using 32khz counter or
  * external timer source, but specifically not CP0 Counter. */
 int allow_au1k_wait;
@@ -132,7 +153,6 @@ static inline void check_wait(void)
         case CPU_R4700:
         case CPU_R5000:
         case CPU_NEVADA:
-        case CPU_RM7000:
         case CPU_4KC:
         case CPU_4KEC:
         case CPU_4KSC:
@@ -142,6 +162,10 @@ static inline void check_wait(void)
                 cpu_wait = r4k_wait;
                 break;
 
+        case CPU_RM7000:
+                cpu_wait = rm7k_wait_irqoff;
+                break;
+
         case CPU_24K:
         case CPU_34K:
                 cpu_wait = r4k_wait;