powerpc/e500: fix breakage with fsl_rio_mcheck_exception

The wrong MCSR bit was being used on e500mc.  MCSR_BUS_RBERR only exists
on e500v1/v2.  Use MCSR_LD on e500mc, and remove all MCSR checking
in fsl_rio_mcheck_exception as we now no longer call that function
if the appropriate bit in MCSR is not set.

If RIO support was enabled at compile-time, but was never probed, just
return from fsl_rio_mcheck_exception rather than dereference a NULL
pointer.

TODO: There is still a remaining, though comparitively minor, issue in
that this recovery mechanism will falsely engage if there's an unrelated
MCSR_LD event at the same time as a RIO error.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

2 files changed, 19 insertions, 18 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 0ff4ab98d50c..6414a0d5ba65 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -425,7 +425,7 @@ int machine_check_e500mc(struct pt_regs *regs)
         unsigned long reason = mcsr;
         int recoverable = 1;
 
-        if (reason & MCSR_BUS_RBERR) {
+        if (reason & MCSR_LD) {
                 recoverable = fsl_rio_mcheck_exception(regs);
                 if (recoverable == 1)
                         goto silent_out;
diff --git a/arch/powerpc/sysdev/fsl_rio.c b/arch/powerpc/sysdev/fsl_rio.c
index 5b206a2fe17c..b3fd081d56f5 100644
--- a/arch/powerpc/sysdev/fsl_rio.c
+++ b/arch/powerpc/sysdev/fsl_rio.c
@@ -283,23 +283,24 @@ static void __iomem *rio_regs_win;
 #ifdef CONFIG_E500
 int fsl_rio_mcheck_exception(struct pt_regs *regs)
 {
-        const struct exception_table_entry *entry = NULL;
-        unsigned long reason = mfspr(SPRN_MCSR);
-
-        if (reason & MCSR_BUS_RBERR) {
-                reason = in_be32((u32 *)(rio_regs_win + RIO_LTLEDCSR));
-                if (reason & (RIO_LTLEDCSR_IER | RIO_LTLEDCSR_PRT)) {
-                        /* Check if we are prepared to handle this fault */
-                        entry = search_exception_tables(regs->nip);
-                        if (entry) {
-                                pr_debug("RIO: %s - MC Exception handled\n",
-                                         __func__);
-                                out_be32((u32 *)(rio_regs_win + RIO_LTLEDCSR),
-                                         0);
-                                regs->msr |= MSR_RI;
-                                regs->nip = entry->fixup;
-                                return 1;
-                        }
+        const struct exception_table_entry *entry;
+        unsigned long reason;
+
+        if (!rio_regs_win)
+                return 0;
+
+        reason = in_be32((u32 *)(rio_regs_win + RIO_LTLEDCSR));
+        if (reason & (RIO_LTLEDCSR_IER | RIO_LTLEDCSR_PRT)) {
+                /* Check if we are prepared to handle this fault */
+                entry = search_exception_tables(regs->nip);
+                if (entry) {
+                        pr_debug("RIO: %s - MC Exception handled\n",
+                                 __func__);
+                        out_be32((u32 *)(rio_regs_win + RIO_LTLEDCSR),
+                                 0);
+                        regs->msr |= MSR_RI;
+                        regs->nip = entry->fixup;
+                        return 1;
                 }
         }