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Subject: Re: [PATCH 0/6] Tracing register accesses with pstore and dynamic
 debug
From:   Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     Tom Zanussi <tom.zanussi@linux.intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vivek Gautam <vivek.gautam@codeaurora.org>,
        Prasad Sodagudi <psodagud@codeaurora.org>,
        Ingo Molnar <mingo@kernel.org>, tsoni@codeaurora.org,
        Anton Vorontsov <anton@enomsg.org>,
        Ingo Molnar <mingo@redhat.com>,
        Sibi Sankar <sibis@codeaurora.org>,
        Laura Abbott <labbott@redhat.com>, devicetree@vger.kernel.org,
        Kees Cook <keescook@chromium.org>,
        Arnd Bergmann <arnd@arndb.de>, linux-arm-msm@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        Jason Baron <jbaron@akamai.com>,
        Rob Herring <robh+dt@kernel.org>,
        Tingwei Zhang <tingwei@codeaurora.org>,
        linux-arm-kernel@lists.infradead.org,
        Tony Luck <tony.luck@intel.com>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        Jim Cromie <jim.cromie@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org,
        Bryan Huntsman <bryanh@codeaurora.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Colin Cross <ccross@android.com>,
        Joe Perches <joe@perches.com>, tkjos@google.com
References: <cover.1536430404.git.saiprakash.ranjan@codeaurora.org>
 <20181020052535.GA155509@joelaf.mtv.corp.google.com>
 <1d3ddbe3-d3ac-aa3e-fc9e-36739ddd0c91@codeaurora.org>
 <20181020162719.GA49955@joelaf.mtv.corp.google.com>
 <15ec736d-bd54-5519-4b99-47dd161bc556@codeaurora.org>
Message-ID: <92075d3d-1ea9-d746-384a-1b61ceefcb70@codeaurora.org>
Date:   Sun, 21 Oct 2018 10:29:17 +0530
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On 10/21/2018 9:16 AM, Sai Prakash Ranjan wrote:
> On 10/20/2018 9:57 PM, Joel Fernandes wrote:
>> On Sat, Oct 20, 2018 at 12:02:37PM +0530, Sai Prakash Ranjan wrote:
>>> On 10/20/2018 10:55 AM, Joel Fernandes wrote:
>>>> On Sun, Sep 09, 2018 at 01:57:01AM +0530, Sai Prakash Ranjan wrote:
>>>>> Hi,
>>>>>
>>>>> This patch series adds Event tracing support to pstore and is 
>>>>> continuation
>>>>> to the RFC patch introduced to add a new tracing facility for register
>>>>> accesses called Register Trace Buffer(RTB). Since we decided to not 
>>>>> introduce
>>>>> a separate framework to trace register accesses and use existing 
>>>>> framework
>>>>> like tracepoints, I have moved from RFC. Details of the RFC in link 
>>>>> below:
>>>>>
>>>>> Link: 
>>>>> https://lore.kernel.org/lkml/cover.1535119710.git.saiprakash.ranjan@codeaurora.org/ 
>>>>>
>>>>>
>>>>> MSR tracing example given by Steven was helpful in using 
>>>>> tracepoints for
>>>>> register accesses instead of using separate trace. But just having 
>>>>> these
>>>>> IO traces would not help much unless we could have them in some 
>>>>> persistent
>>>>> ram buffer for debugging unclocked access or some kind of bus hang 
>>>>> or an
>>>>> unexpected reset caused by some buggy driver which happens a lot 
>>>>> during
>>>>> initial development stages. By analyzing the last few entries of 
>>>>> this buffer,
>>>>> we could identify the register access which is causing the issue.
>>>>
>>>> Hi Sai,
>>>>
>>>> I wanted to see if I could make some time to get your patches 
>>>> working. We are
>>>> hitting usecases that need something like this as well. Basically 
>>>> devices
>>>> hanging and then the ramdump does not tell us much, so in this case 
>>>> pstore
>>>> events can be really helpful. This usecase came up last year as well.
>>>>
>>>> Anyway while I was going through your patches, I cleaned up some 
>>>> pstore code
>>>> as well and I have 3 more patches on top of yours for this clean up. 
>>>> I prefer
>>>> we submit the patches together and sync our work together so that 
>>>> there is
>>>> least conflict.
>>>>
>>>> Here's my latest tree:
>>>> https://github.com/joelagnel/linux-kernel/commits/pstore-events
>>>> (note that I have only build tested the patches since I just wrote 
>>>> them and
>>>> its quite late in the night here ;-))
>>>>
>>>
>>> Hi Joel,
>>>
>>> Thanks for looking into this. Sure, I will be happy to sync up with 
>>> you on
>>
>> Thanks. And added a fourth patch in the tree too.
>>
>>> this. I can test your additional patches on top of my pstore patches. 
>>> BTW,
>>> I'm still stuck at copying binary record into pstore and then extract it
>>> during read time. Seems like I'm missing something.
>>
>> Sure, push your latest somewhere and let me know. I'll try to get you 
>> unstuck.
>>
> 
> Thanks Joel, I will push my changes and let you know in some time.
> 

Hi Joel,

Here's my tree:
https://github.com/saiprakash-ranjan/linux/commits/pstore-events

I have one patch extra on top of your patches. Nothing much on binary 
record storage in this patch, only removed kmalloc in pstore event call 
to avoid loop.

Thanks,
Sai
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