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

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Date:   Wed, 28 Oct 2020 22:09:42 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     mathieu.poirier@...aro.org, mike.leach@...aro.org,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH v3 23/26] 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.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 .../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