linux-kernel - Re: [PATCH 2/4] coresight: trbe: Work around the ignored system register writes

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Message-ID: <0020da84-ce90-f269-27e1-6a6c90f6317b@arm.com>
Date:   Wed, 5 Jan 2022 10:01:00 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        coresight@...ts.linaro.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] coresight: trbe: Work around the ignored system
 register writes

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@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Suzuki Poulose <suzuki.poulose@....com>
> Cc: coresight@...ts.linaro.org
> Cc: linux-doc@...r.kernel.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....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