coresight: etm4x: Detect system instructions support

ETM v4.4 onwards adds support for system instruction access
to the ETM. Detect the support on an ETM and switch to using the
mode when available.

Link: https://lore.kernel.org/r/20210110224850.1880240-23-suzuki.poulose@arm.com
Cc: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210201181351.1475223-25-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -782,6 +782,37 @@ static const struct coresight_ops etm4_cs_ops = {
 	.source_ops	= &etm4_source_ops,
 };
 
+static inline bool cpu_supports_sysreg_trace(void)
+{
+	u64 dfr0 = read_sysreg_s(SYS_ID_AA64DFR0_EL1);
+
+	return ((dfr0 >> ID_AA64DFR0_TRACEVER_SHIFT) & 0xfUL) > 0;
+}
+
+static bool etm4_init_sysreg_access(struct etmv4_drvdata *drvdata,
+				    struct csdev_access *csa)
+{
+	u32 devarch;
+
+	if (!cpu_supports_sysreg_trace())
+		return false;
+
+	/*
+	 * ETMs implementing sysreg access must implement TRCDEVARCH.
+	 */
+	devarch = read_etm4x_sysreg_const_offset(TRCDEVARCH);
+	if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH)
+		return false;
+	*csa = (struct csdev_access) {
+		.io_mem	= false,
+		.read	= etm4x_sysreg_read,
+		.write	= etm4x_sysreg_write,
+	};
+
+	drvdata->arch = etm_devarch_to_arch(devarch);
+	return true;
+}
+
 static bool etm4_init_iomem_access(struct etmv4_drvdata *drvdata,
 				   struct csdev_access *csa)
 {
@@ -812,9 +843,17 @@ static bool etm4_init_iomem_access(struct etmv4_drvdata *drvdata,
 static bool etm4_init_csdev_access(struct etmv4_drvdata *drvdata,
 				   struct csdev_access *csa)
 {
+	/*
+	 * Always choose the memory mapped io, if there is
+	 * a memory map to prevent sysreg access on broken
+	 * systems.
+	 */
 	if (drvdata->base)
 		return etm4_init_iomem_access(drvdata, csa);
 
+	if (etm4_init_sysreg_access(drvdata, csa))
+		return true;
+
 	return false;
 }