coresight: etm: Override TRCIDR3.CCITMIN on errata affected cpus

This work arounds errata 1490853 on Cortex-A76, and Neoverse-N1, errata
1491015 on Cortex-A77, errata 1502854 on Cortex-X1, and errata 1619801 on
Neoverse-V1, based affected cpus, where software read for TRCIDR3.CCITMIN
field in ETM gets an wrong value.

If software uses the value returned by the TRCIDR3.CCITMIN register field,
then it will limit the range which could be used for programming the ETM.
In reality, the ETM could be programmed with a much smaller value than what
is indicated by the TRCIDR3.CCITMIN field and still function correctly.

If software reads the TRCIDR3.CCITMIN register field, corresponding to the
instruction trace counting minimum threshold, observe the value 0x100 or a
minimum cycle count threshold of 256. The correct value should be 0x4 or a
minimum cycle count threshold of 4.

This work arounds the problem via storing 4 in drvdata->ccitmin on affected
systems where the TRCIDR3.CCITMIN has been 256, thus preserving cycle count
threshold granularity.

These errata information has been updated in Documentation/arch/arm64/silicon-errata.rst,
but without their corresponding configs because these have been implemented
directly in the driver.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
[ Fixed location of silicon-errata.rst in commit description ]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230921033631.1298723-2-anshuman.khandual@arm.com

1 files changed, 37 insertions, 0 deletions

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 34aee59dd147..5feb2bd41ee5 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1150,6 +1150,41 @@ static void cpu_detect_trace_filtering(struct etmv4_drvdata *drvdata)
 	drvdata->trfcr = trfcr;
 }
 
+/*
+ * The following errata on applicable cpu ranges, affect the CCITMIN filed
+ * in TCRIDR3 register. Software read for the field returns 0x100 limiting
+ * the cycle threshold granularity, whereas the right value should have
+ * been 0x4, which is well supported in the hardware.
+ */
+static struct midr_range etm_wrong_ccitmin_cpus[] = {
+	/* Erratum #1490853 - Cortex-A76 */
+	MIDR_RANGE(MIDR_CORTEX_A76, 0, 0, 4, 0),
+	/* Erratum #1490853 - Neoverse-N1 */
+	MIDR_RANGE(MIDR_NEOVERSE_N1, 0, 0, 4, 0),
+	/* Erratum #1491015 - Cortex-A77 */
+	MIDR_RANGE(MIDR_CORTEX_A77, 0, 0, 1, 0),
+	/* Erratum #1502854 - Cortex-X1 */
+	MIDR_REV(MIDR_CORTEX_X1, 0, 0),
+	/* Erratum #1619801 - Neoverse-V1 */
+	MIDR_REV(MIDR_NEOVERSE_V1, 0, 0),
+	{},
+};
+
+static void etm4_fixup_wrong_ccitmin(struct etmv4_drvdata *drvdata)
+{
+	/*
+	 * Erratum affected cpus will read 256 as the minimum
+	 * instruction trace cycle counting threshold whereas
+	 * the correct value should be 4 instead. Override the
+	 * recorded value for 'drvdata->ccitmin' to workaround
+	 * this problem.
+	 */
+	if (is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus)) {
+		if (drvdata->ccitmin == 256)
+			drvdata->ccitmin = 4;
+	}
+}
+
 static void etm4_init_arch_data(void *info)
 {
 	u32 etmidr0;
@@ -1214,6 +1249,8 @@ static void etm4_init_arch_data(void *info)
 	etmidr3 = etm4x_relaxed_read32(csa, TRCIDR3);
 	/* CCITMIN, bits[11:0] minimum threshold value that can be programmed */
 	drvdata->ccitmin = FIELD_GET(TRCIDR3_CCITMIN_MASK, etmidr3);
+	etm4_fixup_wrong_ccitmin(drvdata);
+
 	/* EXLEVEL_S, bits[19:16] Secure state instruction tracing */
 	drvdata->s_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_S_MASK, etmidr3);
 	drvdata->config.s_ex_level = drvdata->s_ex_level;