coresight: ptm: Adds trace return stack option programming for PTM.

Adds handling to program the return stack option into PTM hardware if
specified in the perf command line.

If option is not supported by the hardware then it will be ignored.
This allows capture to move between core/ETM combinations that have the
hardware support to those that do not.
Signed-off-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm.h

@@ -106,6 +106,7 @@
 #define ETMTECR1_START_STOP	BIT(25)
 /* ETMCCER - 0x1E8 */
 #define ETMCCER_TIMESTAMP	BIT(22)
+#define ETMCCER_RETSTACK	BIT(23)
 
 #define ETM_MODE_EXCLUDE	BIT(0)
 #define ETM_MODE_CYCACC		BIT(1)

drivers/hwtracing/coresight/coresight-etm3x.c

@@ -310,7 +310,9 @@ void etm_config_trace_mode(struct etm_config *config)
 	config->addr_type[1] = ETM_ADDR_TYPE_RANGE;
 }
 
-#define ETM3X_SUPPORTED_OPTIONS (ETMCR_CYC_ACC | ETMCR_TIMESTAMP_EN)
+#define ETM3X_SUPPORTED_OPTIONS (ETMCR_CYC_ACC | \
+				 ETMCR_TIMESTAMP_EN | \
+				 ETMCR_RETURN_STACK)
 
 static int etm_parse_event_config(struct etm_drvdata *drvdata,
 				  struct perf_event *event)
@@ -341,14 +343,24 @@ static int etm_parse_event_config(struct etm_drvdata *drvdata,
 		etm_config_trace_mode(config);
 
 	/*
-	 * At this time only cycle accurate and timestamp options are
-	 * available.
+	 * At this time only cycle accurate, return stack  and timestamp
+	 * options are available.
 	 */
 	if (attr->config & ~ETM3X_SUPPORTED_OPTIONS)
 		return -EINVAL;
 
 	config->ctrl = attr->config;
 
+	/*
+	 * Possible to have cores with PTM (supports ret stack) and ETM
+	 * (never has ret stack) on the same SoC. So if we have a request
+	 * for return stack that can't be honoured on this core then
+	 * clear the bit - trace will still continue normally
+	 */
+	if ((config->ctrl & ETMCR_RETURN_STACK) &&
+	    !(drvdata->etmccer & ETMCCER_RETSTACK))
+		config->ctrl &= ~ETMCR_RETURN_STACK;
+
 	return 0;
 }