[PATCH v3 23/26] coresight: etm4x: Detect system instructions support

[Suzuki K Poulose]

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.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
---
 .../coresight/coresight-etm4x-core.c          | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 4bc2f15b6332..dc537b5612eb 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -675,6 +675,37 @@ 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 etm_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 etm_init_iomem_access(struct etmv4_drvdata *drvdata,
 				  struct csdev_access *csa)
 {
@@ -705,9 +736,17 @@ static bool etm_init_iomem_access(struct etmv4_drvdata *drvdata,
 static bool etm_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 etm_init_iomem_access(drvdata, csa);
 
+	if (etm_init_sysreg_access(drvdata, csa))
+		return true;
+
 	return false;
 }
 
-- 
2.24.1