linux-kernel - Re: [PATCH v10 8/8] Documentation: coresight: Panic support

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Message-ID: <20240919020949.GA735454@hyd1403.caveonetworks.com>
Date: Thu, 19 Sep 2024 07:39:49 +0530
From: Linu Cherian <lcherian@...vell.com>
To: Bagas Sanjaya <bagasdotme@...il.com>
CC: <suzuki.poulose@....com>, <mike.leach@...aro.org>, <james.clark@....com>,
        <linux-arm-kernel@...ts.infradead.org>, <coresight@...ts.linaro.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
        <corbet@....net>, <devicetree@...r.kernel.org>, <sgoutham@...vell.com>,
        <gcherian@...vell.com>
Subject: Re: [PATCH v10 8/8] Documentation: coresight: Panic support

Hi,

On 2024-09-17 at 07:16:46, Bagas Sanjaya (bagasdotme@...il.com) wrote:
> On Mon, Sep 16, 2024 at 04:04:37PM +0530, Linu Cherian wrote:
> > +3. On a kernel panic, all coresight blocks are disabled, necessary
> > +   metadata is synced by kernel panic handler.
> "... and necessary metadata ..."
> > +
> > +   System would eventually reboot or boot a crashdump kernel.
> > +
> > +4. For  platforms that supports crashdump kernel, raw trace data can be
> > +   dumped using the coresight sysfs interface from the crashdump kernel
> > +   itself. Persistent RAM is not a requirement in this case.
> > +
> > +5. For platforms that supports persistent RAM, trace data can be dumped
> > +   using the coresight sysfs interface in the subsequent Linux boot.
> > +   Crashdump kernel is not a requirement in this case. Persistent RAM
> > +   ensures that trace data is intact across reboot.
> > +
> > +Coresight trace during Watchdog reset
> > +-------------------------------------
> > +The main difference between addressing the watchdog reset and kernel panic
> > +case are below,
> "... are:"
> > +Sample commands for testing a Kernel panic case with ETR sink
> > +-------------------------------------------------------------
> > +
> > +1. Boot Linux kernel with "crash_kexec_post_notifiers" added to the kernel
> > +   bootargs. This is mandatory if the user would like to read the tracedata
> > +   from the crashdump kernel.
> > +
> > +2. Enable the preloaded ETM configuration
> > +
> > +    #echo 1 > /sys/kernel/config/cs-syscfg/configurations/panicstop/enable
> > +
> > +3. Configure CTI using sysfs interface::
> > +
> > +    #./cti_setup.sh
> > +
> > +    #cat cti_setup.sh
> > +
> > +
> > +    cd /sys/bus/coresight/devices/
> > +
> > +    ap_cti_config () {
> > +      #ETM trig out[0] trigger to Channel 0
> > +      echo 0 4 > channels/trigin_attach
> > +    }
> > +
> > +    etf_cti_config () {
> > +      #ETF Flush in trigger from Channel 0
> > +      echo 0 1 > channels/trigout_attach
> > +      echo 1 > channels/trig_filter_enable
> > +    }
> > +
> > +    etr_cti_config () {
> > +      #ETR Flush in from Channel 0
> > +      echo 0 1 > channels/trigout_attach
> > +      echo 1 > channels/trig_filter_enable
> > +    }
> > +
> > +    ctidevs=`find . -name "cti*"`
> > +
> > +    for i in $ctidevs
> > +    do
> > +            cd $i
> > +
> > +            connection=`find . -name "ete*"`
> > +            if [ ! -z "$connection" ]
> > +            then
> > +                    echo "AP CTI config for $i"
> > +                    ap_cti_config
> > +            fi
> > +
> > +            connection=`find . -name "tmc_etf*"`
> > +            if [ ! -z "$connection" ]
> > +            then
> > +                    echo "ETF CTI config for $i"
> > +                    etf_cti_config
> > +            fi
> > +
> > +            connection=`find . -name "tmc_etr*"`
> > +            if [ ! -z "$connection" ]
> > +            then
> > +                    echo "ETR CTI config for $i"
> > +                    etr_cti_config
> > +            fi
> > +
> > +            cd ..
> > +    done
> > +
> > +Note: CTI connections are SOC specific and hence the above script is
> > +added just for reference.
> > +
> > +4. Choose reserved buffer mode for ETR buffer
> > +    #echo "resrv" > /sys/bus/coresight/devices/tmc_etr0/buf_mode_preferred
> > +
> > +5. Enable stop on flush trigger configuration
> > +    #echo 1 > /sys/bus/coresight/devices/tmc_etr0/stop_on_flush
> > +
> > +6. Start Coresight tracing on cores 1 and 2 using sysfs interface
> > +
> > +7. Run some application on core 1
> > +    #taskset -c 1 dd if=/dev/urandom of=/dev/null &
> > +
> > +8. Invoke kernel panic on core 2
> > +    #echo 1 > /proc/sys/kernel/panic
> > +    #taskset -c 2 echo c > /proc/sysrq-trigger
> > +
> > +9. From rebooted kernel or crashdump kernel, read crashdata
> > +
> > +    #dd if=/dev/crash_tmc_etr0 of=/trace/cstrace.bin
> > +
> > +10. Run opencsd decoder tools/scripts to generate the instruction trace.
> 
> Format all command lines as literal code blocks to be consistent:
> 
> ---- >8 ----
> diff --git a/Documentation/trace/coresight/panic.rst b/Documentation/trace/coresight/panic.rst
> index 3b53d91cace8fd..864f6c05b3f7af 100644
> --- a/Documentation/trace/coresight/panic.rst
> +++ b/Documentation/trace/coresight/panic.rst
> @@ -113,7 +113,7 @@ Sample commands for testing a Kernel panic case with ETR sink
>     bootargs. This is mandatory if the user would like to read the tracedata
>     from the crashdump kernel.
>  
> -2. Enable the preloaded ETM configuration
> +2. Enable the preloaded ETM configuration::
>  
>      #echo 1 > /sys/kernel/config/cs-syscfg/configurations/panicstop/enable
>  
> @@ -176,22 +176,26 @@ Sample commands for testing a Kernel panic case with ETR sink
>  Note: CTI connections are SOC specific and hence the above script is
>  added just for reference.
>  
> -4. Choose reserved buffer mode for ETR buffer
> +4. Choose reserved buffer mode for ETR buffer::
> +
>      #echo "resrv" > /sys/bus/coresight/devices/tmc_etr0/buf_mode_preferred
>  
> -5. Enable stop on flush trigger configuration
> +5. Enable stop on flush trigger configuration::
> +
>      #echo 1 > /sys/bus/coresight/devices/tmc_etr0/stop_on_flush
>  
>  6. Start Coresight tracing on cores 1 and 2 using sysfs interface
>  
> -7. Run some application on core 1
> +7. Run some application on core 1::
> +
>      #taskset -c 1 dd if=/dev/urandom of=/dev/null &
>  
> -8. Invoke kernel panic on core 2
> +8. Invoke kernel panic on core 2::
> +
>      #echo 1 > /proc/sys/kernel/panic
>      #taskset -c 2 echo c > /proc/sysrq-trigger
>  
> -9. From rebooted kernel or crashdump kernel, read crashdata
> +9. From rebooted kernel or crashdump kernel, read crashdata::
>  
>      #dd if=/dev/crash_tmc_etr0 of=/trace/cstrace.bin


Ack.

>  
> Thanks.
> 
> -- 
> An old man doll... just what I always wanted! - Clara

Linu Cherian.