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From:   Mike Leach <mike.leach@linaro.org>
Date:   Tue, 19 Sep 2023 12:06:16 +0100
Message-ID: <CAJ9a7VghAjdKU90NoR4VfAr+dr2GmzrwNCT23jzKMpdiwNzd-Q@mail.gmail.com>
Subject: Re: [PATCH V5 - RESEND 1/3] coresight: etm: Override TRCIDR3.CCITMIN
 on errata affected cpus
To:     Anshuman Khandual <anshuman.khandual@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, suzuki.poulose@arm.com,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        James Clark <james.clark@arm.com>,
        Leo Yan <leo.yan@linaro.org>, Jonathan Corbet <corbet@lwn.net>,
        linux-doc@vger.kernel.org, coresight@lists.linaro.org,
        linux-kernel@vger.kernel.org
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On Fri, 15 Sept 2023 at 10:37, Anshuman Khandual
<anshuman.khandual@arm.com> 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@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
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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);
> +}
> +
>  static void etm4_init_arch_data(void *info)
>  {
>         u32 etmidr0;
> @@ -1214,6 +1247,9 @@ 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;
> +
>         /* 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
>
Reviewed by: Mike Leach <mike.leach@linaro.org>

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK