ARM: 6294/1: etm: do a dummy read from OSSRR during initialization

The first read from ETM OS save and restore register after the power
down bit deassertion returns garbage.

Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NAlexander Shishkin <virtuoso@slind.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/etm.c

@@ -543,7 +543,9 @@ static int __init etm_probe(struct amba_device *dev, struct amba_id *id)
 	t->etm_portsz = 1;
 
 	etm_unlock(t);
-	ret = etm_readl(t, ETMMR_PDSR);
+	(void)etm_readl(t, ETMMR_PDSR);
+	/* dummy first read */
+	(void)etm_readl(&tracer, ETMMR_OSSRR);
 
 	t->ncmppairs = etm_readl(t, ETMR_CONFCODE) & 0xf;
 	etm_writel(t, 0x440, ETMR_CTRL);