Re: [PATCH V3 1/3] coresight: etm: Override TRCIDR3.CCITMIN on errata affected cpus
From: Suzuki K Poulose
Date: Fri Aug 11 2023 - 05:31:48 EST
On 11/08/2023 10:03, Mike Leach wrote:
Hi Anshuman,
A few minor points.
On Fri, 11 Aug 2023 at 04:46, Anshuman Khandual
<anshuman.khandual@xxxxxxx> wrote:
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 arch/arm64/silicon-errata.rst,
but without their corresponding configs because these have been implemented
directly in the driver.
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cc: Mike Leach <mike.leach@xxxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: coresight@xxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
Documentation/arch/arm64/silicon-errata.rst | 10 +++++
.../coresight/coresight-etm4x-core.c | 37 +++++++++++++++++++
2 files changed, 47 insertions(+)
diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
index bedd3a1d7b42..b08f33eda5f1 100644
--- a/Documentation/arch/arm64/silicon-errata.rst
+++ b/Documentation/arch/arm64/silicon-errata.rst
@@ -107,6 +107,10 @@ stable kernels.
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-A76 | #1463225 | ARM64_ERRATUM_1463225 |
+----------------+-----------------+-----------------+-----------------------------+
+| ARM | Cortex-A76 | #1490853 | N/A |
++----------------+-----------------+-----------------+-----------------------------+
+| ARM | Cortex-A77 | #1491015 | N/A |
++----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-A77 | #1508412 | ARM64_ERRATUM_1508412 |
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-A510 | #2051678 | ARM64_ERRATUM_2051678 |
@@ -125,6 +129,8 @@ stable kernels.
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-A715 | #2645198 | ARM64_ERRATUM_2645198 |
+----------------+-----------------+-----------------+-----------------------------+
+| ARM | Cortex-X1 | #1502854 | N/A |
++----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-X2 | #2119858 | ARM64_ERRATUM_2119858 |
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Cortex-X2 | #2224489 | ARM64_ERRATUM_2224489 |
@@ -133,6 +139,8 @@ stable kernels.
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Neoverse-N1 | #1349291 | N/A |
+----------------+-----------------+-----------------+-----------------------------+
+| ARM | Neoverse-N1 | #1490853 | N/A |
++----------------+-----------------+-----------------+-----------------------------+
| ARM | Neoverse-N1 | #1542419 | ARM64_ERRATUM_1542419 |
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Neoverse-N2 | #2139208 | ARM64_ERRATUM_2139208 |
@@ -141,6 +149,8 @@ stable kernels.
+----------------+-----------------+-----------------+-----------------------------+
| ARM | Neoverse-N2 | #2253138 | ARM64_ERRATUM_2253138 |
+----------------+-----------------+-----------------+-----------------------------+
+| ARM | Neoverse-V1 | #1619801 | N/A |
++----------------+-----------------+-----------------+-----------------------------+
| ARM | MMU-500 | #841119,826419 | N/A |
+----------------+-----------------+-----------------+-----------------------------+
| ARM | MMU-600 | #1076982,1209401| N/A |
Could these doc changes not go in patch 3?
I believe no, because this patch works around the erratum and it will
help anybody looking for the workaround using the list above + the patch
3 is not related to the erratum. It is simply documenting the new perf
option.
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 703b6fcbb6a5..1f3d29a639ff 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1150,6 +1150,31 @@ static void cpu_detect_trace_filtering(struct etmv4_drvdata *drvdata)
drvdata->trfcr = trfcr;
}
+/*
+ * The following errata on applicable cpu rangess affect the CCITMIN filed
s/rangess/ranges
+ * in TCRIDR3 register. Software read for the field returns 0x100 limiting
+ * the cycle threshold granularity, where as 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 bool etm4_work_around_wrong_ccitmin(void)
This is not the actual work around - perhaps this should be
etm4_core_reads_wrong_ccitmin()?
+{
+ return is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus);
+}
+
static void etm4_init_arch_data(void *info)
{
u32 etmidr0;
@@ -1214,6 +1239,18 @@ 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);
+ if (etm4_work_around_wrong_ccitmin()) {
+ /*
+ * Erratum affected cpus will read 256 as the minimum
+ * instruction trace cycle counting threshold where as
+ * the correct value should be 4 instead. Override the
+ * recorded value for 'drvdata->ccitmin' to workaround
+ * this problem.
+ */
+ if (drvdata->ccitmin == 256) >
Not sure this check matters - fixed cores will be 4, non fixed cores
as identified by the list need to be 4, we don't care what the read
value is if the core is on the list.
To be on the safer side, we may allow a core to have ccitmin more than
0x4 if we only fixup what is documented per erratum. So this looks fine
to me.
Suzuki
+ drvdata->ccitmin = 4;
+ }
+
/* 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;
--
2.25.1
Regards
Mike