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Message-ID: <CAJ9a7VhyKjLtRfg09GWKs5k0QfQK7mix8H8MB5ObF5ADB=RC-w@mail.gmail.com>
Date: Wed, 20 Sep 2023 09:49:35 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
linux-arm-kernel@...ts.infradead.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
James Clark <james.clark@....com>,
Leo Yan <leo.yan@...aro.org>, Jonathan Corbet <corbet@....net>,
linux-doc@...r.kernel.org, coresight@...ts.linaro.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 - RESEND 1/3] coresight: etm: Override TRCIDR3.CCITMIN
on errata affected cpus
On Wed, 20 Sept 2023 at 07:40, Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
>
>
> On 9/19/23 16:56, Suzuki K Poulose wrote:
> > Hi Anshuman
> >
> > On 15/09/2023 10:36, 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.
> >>
> >
> > The patch looks good to me, please find a minor change below.
> >
> >> 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@....com>
> >> Cc: Will Deacon <will@...nel.org>
> >> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> >> Cc: Mike Leach <mike.leach@...aro.org>
> >> Cc: James Clark <james.clark@....com>
> >> Cc: Jonathan Corbet <corbet@....net>
> >> Cc: linux-doc@...r.kernel.org
> >> Cc: coresight@...ts.linaro.org
> >> Cc: linux-arm-kernel@...ts.infradead.org
> >> Cc: linux-kernel@...r.kernel.org
> >> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> >> ---
> >> Documentation/arch/arm64/silicon-errata.rst | 10 ++++++
> >> .../coresight/coresight-etm4x-core.c | 36 +++++++++++++++++++
> >> 2 files changed, 46 insertions(+)
> >>
> >> diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
> >> index e96f057ea2a0..8f1be5da68b7 100644
> >> --- a/Documentation/arch/arm64/silicon-errata.rst
> >> +++ b/Documentation/arch/arm64/silicon-errata.rst
> >> @@ -115,6 +115,10 @@ 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-A710 | #2119858 | ARM64_ERRATUM_2119858 |
> >> @@ -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 |
> >> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> index 77b0271ce6eb..c01455bb1caf 100644
> >> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> @@ -1150,6 +1150,39 @@ 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, 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 bool etm4_core_reads_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.
> >> + */
> >> + return is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus) &&
> >> + (drvdata->ccitmin == 256);
> >
> > minor nit: Having looked at this, it feels like, fixing the ccitmin
> > value to 4, could be moved into this function. Otherwise, we have all
> > the required information about the erratum and the real application of
> > work around is left in the caller, which kind of feels disconnected.
> >
> > So, please could we rename the above function to:
> >
> > static void etm4_fixup_wrong_ccitmin(str..)
> > {
> > /* Comment as above */
> > if (....)
> > drvdata->ccitmin = 4;
> > }
>
> I will fold in the following change for the patch. Please do let me
> know if this reflects your suggestions accurately. Also planning to
> carry Mike's tag after the change.
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 044aed25979b..5b6a878a2ac5 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1175,7 +1175,7 @@ static struct midr_range etm_wrong_ccitmin_cpus[] = {
> {},
> };
>
> -static bool etm4_core_reads_wrong_ccitmin(struct etmv4_drvdata *drvdata)
> +static void etm4_fixup_wrong_ccitmin(struct etmv4_drvdata *drvdata)
> {
> /*
> * Erratum affected cpus will read 256 as the minimum
> @@ -1184,8 +1184,10 @@ static bool etm4_core_reads_wrong_ccitmin(struct etmv4_drvdata *drvdata)
> * recorded value for 'drvdata->ccitmin' to workaround
> * this problem.
> */
> - return is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus) &&
> - (drvdata->ccitmin == 256);
> + if (is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus)) {
> + if (drvdata->ccitmin == 256)
> + drvdata->ccitmin = 4;
> + }
> }
>
Looks good to me
Mike
> static void etm4_init_arch_data(void *info)
> @@ -1252,8 +1254,7 @@ 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_core_reads_wrong_ccitmin(drvdata))
> - drvdata->ccitmin = 4;
> + 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);
>
--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK
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