Date:   Mon, 7 Dec 2020 09:00:51 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Qi Liu <liuqi115@...wei.com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        coresight@...ts.linaro.org, linuxarm@...wei.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        mike.leach@...aro.org
Subject: Re: [PATCH v5] coresight: etm4x: Modify core-commit of cpu to avoid
 the overflow of HiSilicon ETM

On Mon, Dec 07, 2020 at 07:32:21PM +0800, Qi Liu wrote:
> 
> 
> On 2020/12/7 19:27, Suzuki K Poulose wrote:
> > 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@...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.
> >>>>>> 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
> > 
> > .
> ok, I'll send a new version. :)
> 

Please do so by tomorrow morning (North America time) if you want to see this
going in the v5.11 merge window.  Otherwise it will be another 3 months.

> Thanks
> Qi
> > 
> 
> 
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