Blackfin: workaround anomaly 05000310

While fetching instructions at the boundary of L1 instruction SRAM, a false
External Memory Addressing Error might be triggered.  We should ignore this
and continue on our way to avoid random crashes.

Because hardware errors are not exact in the Blackfin architecture, we need
to catch a few more common cases when the code flow changes and the signal
is finally delivered.

Signed-off-by: Barry Song <barry.song@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/kernel/traps.c

@@ -524,6 +524,36 @@ asmlinkage notrace void trap_c(struct pt_regs *fp)
 			break;
 		/* External Memory Addressing Error */
 		case (SEQSTAT_HWERRCAUSE_EXTERN_ADDR):
+			if (ANOMALY_05000310) {
+				static unsigned long anomaly_rets;
+
+				if ((fp->pc >= (L1_CODE_START + L1_CODE_LENGTH - 512)) &&
+				    (fp->pc < (L1_CODE_START + L1_CODE_LENGTH))) {
+					/*
+					 * A false hardware error will happen while fetching at
+					 * the L1 instruction SRAM boundary.  Ignore it.
+					 */
+					anomaly_rets = fp->rets;
+					goto traps_done;
+				} else if (fp->rets == anomaly_rets) {
+					/*
+					 * While boundary code returns to a function, at the ret
+					 * point, a new false hardware error might occur too based
+					 * on tests.  Ignore it too.
+					 */
+					goto traps_done;
+				} else if ((fp->rets >= (L1_CODE_START + L1_CODE_LENGTH - 512)) &&
+				           (fp->rets < (L1_CODE_START + L1_CODE_LENGTH))) {
+					/*
+					 * If boundary code calls a function, at the entry point,
+					 * a new false hardware error maybe happen based on tests.
+					 * Ignore it too.
+					 */
+					goto traps_done;
+				} else
+					anomaly_rets = 0;
+			}
+
 			info.si_code = BUS_ADRERR;
 			sig = SIGBUS;
 			strerror = KERN_NOTICE HWC_x3(KERN_NOTICE);