coresight: etm4x: Fix number of resources check for ETM 4.3 and above

The initialisation code checks TRCIDR4 to determine the number of resource
selectors available on the system. Since ETM v 4.3, the value 0 has a
different meaning. This patch takes into account this change.

Signed-off-by: Mike Leach <[e-mail]>
[Removed '.' in patch title, added stable]
Signed-off-by: Mathieu Poirier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/hwtracing/coresight/coresight-etm4x.c

···
 	 * The number of resource pairs conveyed by the HW starts at 0, i.e a
 	 * value of 0x0 indicate 1 resource pair, 0x1 indicate two and so on.
 	 * As such add 1 to the value of NUMRSPAIR for a better representation.
+	 *
+	 * For ETM v4.3 and later, 0x0 means 0, and no pairs are available -
+	 * the default TRUE and FALSE resource selectors are omitted.
+	 * Otherwise for values 0x1 and above the number is N + 1 as per v4.2.
 	 */
-	drvdata->nr_resource = BMVAL(etmidr4, 16, 19) + 1;
+	drvdata->nr_resource = BMVAL(etmidr4, 16, 19);
+	if ((drvdata->arch < ETM4X_ARCH_4V3) || (drvdata->nr_resource > 0))
+		drvdata->nr_resource += 1;
 	/*
 	 * NUMSSCC, bits[23:20] the number of single-shot
 	 * comparator control for tracing. Read any status regs as these

drivers/hwtracing/coresight/coresight-etm4x.h

···
 /* NS MON (EL3) mode never implemented */
 #define ETM_EXLEVEL_NS_VICTLR_MASK	GENMASK(22, 20)
 
+/* Interpretation of resource numbers change at ETM v4.3 architecture */
+#define ETM4X_ARCH_4V3	0x43
+
 /**
  * struct etmv4_config - configuration information related to an ETMv4
  * @mode:	Controls various modes supported by this ETM.