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Date:   Fri, 23 Oct 2020 11:40:54 +0100
From:   Suzuki Poulose <suzuki.poulose@....com>
To:     Qi Liu <liuqi115@...wei.com>, mathieu.poirier@...aro.org,
        Al.Grant@....com, mike.leach@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linuxarm@...wei.com
Subject: Re: [PATCH v3] coresight: etm4x: Modify core-commit of cpu to avoid
 the overflow of HiSilicon ETM

On 10/23/20 11:23 AM, Qi Liu wrote:
> The ETM device can't keep up with the core pipeline when cpu core
> is at full speed. This may cause overflow within core and its ETM.
> This is a common phenomenon on ETM devices.
> 
> On HiSilicon Hip08 platform, a specific feature is added to set
> core pipeline. So commit rate can be reduced manually to avoid ETM
> overflow.
> 
> Signed-off-by: Qi Liu <liuqi115@...wei.com>
> ---
> Change since v1:
> - add CONFIG_ETM4X_IMPDEF_FEATURE and CONFIG_ETM4X_IMPDEF_HISILICON
>    to keep specific feature off platforms which don't use it.
> Change since v2:
> - remove some unused variable.
> 
>   drivers/hwtracing/coresight/Kconfig                | 18 ++++++++
>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 50 ++++++++++++++++++++++
>   2 files changed, 68 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> index c119824..9665d70 100644
> --- a/drivers/hwtracing/coresight/Kconfig
> +++ b/drivers/hwtracing/coresight/Kconfig
> @@ -110,6 +110,24 @@ config CORESIGHT_SOURCE_ETM4X
>   	  To compile this driver as a module, choose M here: the
>   	  module will be called coresight-etm4x.
> 
> +config ETM4X_IMPDEF_FEATURE
> +	bool "Control overflow impdef support in CoreSight ETM 4.x driver "
> +	depends on CORESIGHT_SOURCE_ETM4X
> +	help
> +	  This control provides overflow implement define for CoreSight
> +	  ETM 4.x tracer module which could not reduce commit race
> +	  automatically, and could avoid overflow within ETM tracer module
> +	  and its cpu core.
> +
> +config ETM4X_IMPDEF_HISILICON
> +	bool "Control overflow impdef support in HiSilicon ETM 4.x driver "
> +	depends on ETM4X_IMPDEF_FEATURE
> +	help
> +	  This control provides overflow implement define for HiSilicon
> +	  ETM 4.x tracer module of Hip08 platform. Overflow within ETM
> +	  tracer module and its cpu core can be avoided by reducing core
> +	  commit manually.
> +
>   config CORESIGHT_STM
>   	tristate "CoreSight System Trace Macrocell driver"
>   	depends on (ARM && !(CPU_32v3 || CPU_32v4 || CPU_32v4T)) || ARM64
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index abd706b..35f4333 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -103,12 +103,61 @@ struct etm4_enable_arg {
>   	int rc;
>   };
> 
> +#ifdef CONFIG_ETM4X_IMPDEF_FEATURE
> +
> +#ifdef CONFIG_ETM4X_IMPDEF_HISILICON
> +
> +#define HISI_HIP08_CORE_COMMIT_CLEAR	0x3000
> +#define HISI_HIP08_CORE_COMMIT_SHIFT	12
> +static void etm4_hisi_config_core_commit(int flag)

nit: s/int flag/bool enable ?

> +{
> +	u64 val;
> +
> +	asm volatile("mrs %0,s3_1_c15_c2_5" : "=r"(val));
> +	val &= ~HISI_HIP08_CORE_COMMIT_CLEAR;
> +	val |= flag << HISI_HIP08_CORE_COMMIT_SHIFT;
> +	asm volatile("msr s3_1_c15_c2_5,%0" : : "r"(val));

Sorry for missing this out. We don't encourage the above encodings
as it will break on legacy toolchain. So, please could you follow what
we do normally, by using sys_reg() macros to define the encoding and use
read/write_sysreg_s() instead. See arch/arm64/include/asm/sysreg.h


> +}
> +#else
> +static void etm4_hisi_config_core_commit(int flag)
> +{
> +}
> +#endif /* CONFIG_ETM4X_IMPDEF_HISILICON */
> +
> +static void etm4_enable_arch_specific(void)
> +{
> +	/*
> +	 * If ETM device is HiSilicon ETM device, reduce the
> +	 * core-commit to avoid ETM overflow.
> +	 */
> +	etm4_hisi_config_core_commit(1);
> +}
> +
> +static void etm4_disable_arch_specific(void)
> +{
> +	/*
> +	 * If ETM device is HiSilicon ETM device, resume the
> +	 * core-commit after ETM trace is complete.
> +	 */
> +	etm4_hisi_config_core_commit(0);
> +}
> +#else
> +static void etm4_enable_arch_specific(void)
> +{
> +}
> +
> +static void etm4_disable_arch_specific(void)
> +{
> +}
> +#endif /* CONFIG_ETM4X_IMPDEF_FEATURE */
> +
>   static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>   {
>   	int i, rc;
>   	struct etmv4_config *config = &drvdata->config;
>   	struct device *etm_dev = &drvdata->csdev->dev;
> 
> +	etm4_enable_arch_specific();
>   	CS_UNLOCK(drvdata->base);

Please could we move the enable_arch_specific() after the CS_UNLOCK ?
That way any potential code could do something with the ETM4x registers.

> 
>   	etm4_os_unlock(drvdata);
> @@ -475,6 +524,7 @@ static void etm4_disable_hw(void *info)
>   	struct device *etm_dev = &drvdata->csdev->dev;
>   	int i;
> 
> +	etm4_disable_arch_specific();
>   	CS_UNLOCK(drvdata->base);
> 

Same here

Suzuki

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