Hi-- On 8/18/23 04:20, Anshuman Khandual 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 | 36 +++++++++++++++++++ > 2 files changed, 46 insertions(+) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c > index 7e307022303a..591fab73ee79 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c > @@ -1131,6 +1131,39 @@ 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, where as the right value should have whereas > + * 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_core_reads_wrong_ccitmin(struct etmv4_drvdata *drvdata) > +{ > + /* > + * Erratum affected cpus will read 256 as the minimum > + * instruction trace cycle counting threshold where as whereas > + * the correct value should be 4 instead. Override the > + * recorded value for 'drvdata->ccitmin' to workaround > + * this problem. > + */ -- ~Randy