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SubjectRe: [PATCH 2/4] coresight: trbe: Work around the ignored system register writes
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Hi Anshuman

On 05/01/2022 05:05, Anshuman Khandual wrote:
> TRBE implementations affected by Arm erratum #2064142 might fail to write
> into certain system registers after the TRBE has been disabled. Under some
> conditions after TRBE has been disabled, writes into certain TRBE registers
> TRBLIMITR_EL1, TRBPTR_EL1, TRBBASER_EL1, TRBSR_EL1 and TRBTRG_EL1 will be
> ignored and not be effected.
>
> Work around this problem in the TRBE driver by executing TSB CSYNC and DSB
> just after the trace collection has stopped and before performing a system
> register write to one of the affected registers. This adds a new cpu errata
> in arm64 errata framework and also updates TRBE driver as required.
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Suzuki Poulose <suzuki.poulose@arm.com>
> Cc: coresight@lists.linaro.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> Documentation/arm64/silicon-errata.rst | 2 +
> arch/arm64/Kconfig | 18 +++++++
> arch/arm64/kernel/cpu_errata.c | 9 ++++
> arch/arm64/tools/cpucaps | 1 +
> drivers/hwtracing/coresight/coresight-trbe.c | 54 ++++++++++++++------
> drivers/hwtracing/coresight/coresight-trbe.h | 8 ---
> 6 files changed, 68 insertions(+), 24 deletions(-)

I think it may be a good idea to split the patch into
two parts :

- arm64 kernel part. (cpucap defintions and detection)
- trbe driver part

So that it is easier to merge these series upstream to
avoid conflicts.

>
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index 5342e895fb60..c9b30e6c2b6c 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -52,6 +52,8 @@ stable kernels.
> | Allwinner | A64/R18 | UNKNOWN1 | SUN50I_ERRATUM_UNKNOWN1 |
> +----------------+-----------------+-----------------+-----------------------------+
> +----------------+-----------------+-----------------+-----------------------------+
> +| ARM | Cortex-A510 | #2064142 | ARM64_ERRATUM_2064142 |
> ++----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A53 | #826319 | ARM64_ERRATUM_826319 |
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A53 | #827319 | ARM64_ERRATUM_827319 |
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c4207cf9bb17..2105b68d88db 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -778,6 +778,24 @@ config ARM64_ERRATUM_2224489
>
> If unsure, say Y.
>
> +config ARM64_ERRATUM_2064142
> + bool "Cortex-A510: 2064142: workaround TRBE register writes while disabled"
> + depends on CORESIGHT_TRBE
> + default y
> + help
> + This option adds the workaround for ARM Cortex-A510 erratum 2064142.
> +
> + Affected Cortex-A510 core might fail to write into system registers after the
> + TRBE has been disabled. Under some conditions after the TRBE has been disabled
> + writes into TRBE registers TRBLIMITR_EL1, TRBPTR_EL1, TRBBASER_EL1, TRBSR_EL1,
> + and TRBTRG_EL1 will be ignored and will not be effected.
> +
> + Work around this in the driver by executing TSB CSYNC and DSB after collection
> + is stopped and before performing a system register write to one of the affected
> + registers.
> +
> + If unsure, say Y.
> +
> config CAVIUM_ERRATUM_22375
> bool "Cavium erratum 22375, 24313"
> default y
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 9e1c1aef9ebd..cbb7d5a9aee7 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -597,6 +597,15 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
> .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
> CAP_MIDR_RANGE_LIST(trbe_write_out_of_range_cpus),
> },
> +#endif
> +#ifdef CONFIG_ARM64_ERRATUM_2064142
> + {
> + .desc = "ARM erratum 2064142",
> + .capability = ARM64_WORKAROUND_2064142,
> +
> + /* Cortex-A510 r0p0 - r0p2 */
> + ERRATA_MIDR_REV_RANGE(MIDR_CORTEX_A510, 0, 0, 2)
> + },
> #endif
> {
> }
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index 870c39537dd0..fca3cb329e1d 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -55,6 +55,7 @@ WORKAROUND_1418040
> WORKAROUND_1463225
> WORKAROUND_1508412
> WORKAROUND_1542419
> +WORKAROUND_2064142
> WORKAROUND_TRBE_OVERWRITE_FILL_MODE
> WORKAROUND_TSB_FLUSH_FAILURE
> WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 276862c07e32..ec24b62b2cec 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -91,10 +91,12 @@ struct trbe_buf {
> */
> #define TRBE_WORKAROUND_OVERWRITE_FILL_MODE 0
> #define TRBE_WORKAROUND_WRITE_OUT_OF_RANGE 1
> +#define TRBE_WORKAROUND_SYSREG_WRITE_FAILURE 2
>
> static int trbe_errata_cpucaps[] = {
> [TRBE_WORKAROUND_OVERWRITE_FILL_MODE] = ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE,
> [TRBE_WORKAROUND_WRITE_OUT_OF_RANGE] = ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE,
> + [TRBE_WORKAROUND_SYSREG_WRITE_FAILURE] = ARM64_WORKAROUND_2064142,

super minor nit: TRBE_NEEDS_DRAIN_AFTER_DISABLE ?

> -1, /* Sentinel, must be the last entry */
> };
>
> @@ -167,6 +169,11 @@ static inline bool trbe_may_write_out_of_range(struct trbe_cpudata *cpudata)
> return trbe_has_erratum(cpudata, TRBE_WORKAROUND_WRITE_OUT_OF_RANGE);
> }
>
> +static inline bool trbe_may_fail_sysreg_write(struct trbe_cpudata *cpudata)
> +{

minor nit: trbe_needs_drain_after_disable() ?

Either ways, the patch looks good to me.

Suzuki

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