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Subject: Re: [PATCH v5] coresight: etm4x: Modify core-commit of cpu to avoid
 the overflow of HiSilicon ETM
To:     Qi Liu <liuqi115@huawei.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>
Cc:     mike.leach@linaro.org, coresight@lists.linaro.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linuxarm@huawei.com
References: <1606397670-15657-1-git-send-email-liuqi115@huawei.com>
 <20201204185551.GB1424711@xps15>
 <448eb009-da3e-b918-984d-cf563a64f31d@huawei.com>
 <07243eef-dbcf-6500-a66b-5c0e1689ece9@arm.com>
 <0e56f56e-157e-ecf2-bb21-74b79ffdf2ac@huawei.com>
From:   Suzuki K Poulose <suzuki.poulose@arm.com>
Message-ID: <d82f1200-c31f-1040-a630-57e132cabf1b@arm.com>
Date:   Mon, 7 Dec 2020 11:27:16 +0000
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On 12/7/20 11:21 AM, Qi Liu wrote:
> 
> Hi Suzuki,
> On 2020/12/7 18:38, Suzuki K Poulose wrote:
>> On 12/7/20 2:08 AM, Qi Liu wrote:
>>> Hi Mathieu,
>>>
>>> On 2020/12/5 2:55, Mathieu Poirier wrote:
>>>> On Thu, Nov 26, 2020 at 09:34:30PM +0800, 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@huawei.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.
>>>>> Change since v3:
>>>>> - use read/write_sysreg_s() to access register.
>>>>> Change since v4:
>>>>> - rename the call back function to a more generic name, and fix some
>>>>>     compile warnings.
>>>>>
>>>>>    drivers/hwtracing/coresight/Kconfig                |  9 +++
>>>>>    drivers/hwtracing/coresight/coresight-etm4x-core.c | 88 ++++++++++++++++++++++
>>>>>    drivers/hwtracing/coresight/coresight-etm4x.h      |  8 ++
>>>>>    3 files changed, 105 insertions(+)
>>>>>
>>>>> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
>>>>> index c119824..1cc3601 100644
>>>>> --- a/drivers/hwtracing/coresight/Kconfig
>>>>> +++ b/drivers/hwtracing/coresight/Kconfig
>>>>> @@ -110,6 +110,15 @@ 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 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..fcee27a 100644
>>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> @@ -3,6 +3,7 @@
>>>>>     * Copyright (c) 2014, The Linux Foundation. All rights reserved.
>>>>>     */
>>>>>
>>>>> +#include <linux/bitops.h>
>>>>>    #include <linux/kernel.h>
>>>>>    #include <linux/moduleparam.h>
>>>>>    #include <linux/init.h>
>>>>> @@ -28,7 +29,9 @@
>>>>>    #include <linux/perf_event.h>
>>>>>    #include <linux/pm_runtime.h>
>>>>>    #include <linux/property.h>
>>>>> +
>>>>>    #include <asm/sections.h>
>>>>> +#include <asm/sysreg.h>
>>>>>    #include <asm/local.h>
>>>>>    #include <asm/virt.h>
>>>>>
>>>>> @@ -103,6 +106,87 @@ struct etm4_enable_arg {
>>>>>        int rc;
>>>>>    };
>>>>>
>>>>> +#ifdef CONFIG_ETM4X_IMPDEF_FEATURE
>>>>> +
>>>>> +#define HISI_HIP08_AMBA_ID        0x000b6d01
>>>>> +#define ETM4_AMBA_MASK            0xfffff
>>>>> +#define HISI_HIP08_CORE_COMMIT_CLEAR    0x3000
>>>>
>>>> Here bit 12 and 13 are cleared but in etm4_hisi_config_core_commit() only bit 12
>>>> is set - is this intentional?  What is bit 13 for?
>>>>
>>> bit 12 and 13 are used together to set core-commit, 2'b00 means cpu is at full speed,
>>> 2'b01, 2'b10, 2'b11 means reduce the speed of cpu pipeline, and 2'b01 means speed is
>>> reduced to minimum value. So bit 12 and 13 should be cleared together in
>>> etm4_hisi_config_core_commit().
>>
>> Please could you document this in the function.
>>
> of course, thanks.
>>>
>>> Qi
>>>
>>>>> +#define HISI_HIP08_CORE_COMMIT_SHIFT    12
>>>>> +#define HISI_HIP08_CORE_COMMIT_REG    sys_reg(3, 1, 15, 2, 5)
>>>>> +
>>>>> +struct etm4_arch_features {
>>>>> +    void (*arch_callback)(bool enable);
>>>>> +};
>>>>> +
>>>>> +static bool etm4_hisi_match_pid(unsigned int id)
>>>>> +{
>>>>> +    return (id & ETM4_AMBA_MASK) == HISI_HIP08_AMBA_ID;
>>>>> +}
>>>>> +
>>>>> +static void etm4_hisi_config_core_commit(bool enable)
>>>>> +{
>>>>> +    u64 val;
>>>>> +
>>>>> +    val = read_sysreg_s(HISI_HIP08_CORE_COMMIT_REG);
>>>>> +    val &= ~HISI_HIP08_CORE_COMMIT_CLEAR;
>>>>> +    val |= enable << HISI_HIP08_CORE_COMMIT_SHIFT;
>>
>> I would use the explicitly masked values when you update
>> a register.
>>
> ok, how about changing these code to this:
> val &= ~GENMASK(12, 13);

I would do :

// Rename the HISI_HIP08_CORE_COMMIT_CLEAR to HISI_HIP08_CORE_COMMIT_MASK
// above.
#define HISI_HIP08_CORE_COMMIT_MASK		0x3000

#define HISI_HIP08_CORE_COMMIT_FULL		0b00
#define HISI_HIP08_CORE_COMMIT_LVL_1		0b01


u8 commit = enable ? HISI_HIP08_CORE_COMMIT_LVL_1 : HISI_HIP08_CORE_COMMIT_FULL;

...

val |= commit << HISI_HIP08_CORE_COMMIT_SHIFT;

..


Suzuki