From: Dilip Kota <eswara.kota@linux.intel.com>
To: Guenter Roeck <linux@roeck-us.net>,
wim@linux-watchdog.org, linux-watchdog@vger.kernel.org,
devicetree@vger.kernel.org, robbh@kernel.org
Cc: linux-kernel@vger.kernel.org, andriy.shevchenko@intel.com,
cheol.yong.kim@intel.com, qi-ming.wu@intel.com,
yixin.zhu@intel.com
Subject: Re: [PATCH 1/2] dt-bindings: watchdog: intel: Add YAML Schemas for Watchdog timer
Date: Thu, 11 Jun 2020 17:38:14 +0800 [thread overview]
Message-ID: <4feae044-1956-fb70-7786-19c7c48cc391@linux.intel.com> (raw)
In-Reply-To: <c294ced9-a37b-6a90-511e-187bacdec80c@roeck-us.net>
On 6/10/2020 9:05 PM, Guenter Roeck wrote:
> On 6/10/20 12:54 AM, Dilip Kota wrote:
>> On 6/9/2020 9:46 PM, Guenter Roeck wrote:
>>> On 6/9/20 1:57 AM, Dilip Kota wrote:
>>>> On 6/8/2020 9:37 PM, Guenter Roeck wrote:
>>>>> On 6/7/20 10:49 PM, Dilip Kota wrote:
[...]
>>>>>> +
>>>>>> +description: |
>>>>>> + Intel Lightning Mountain SoC has General Purpose Timer Counter(GPTC) which can
>>>>>> + be configured as Clocksource, real time clock and Watchdog timer.
>>>>>> + Each General Purpose Timer Counter has three timers. And total four General
>>>>>> + Purpose Timer Counters are present on Lightning Mountain SoC which sums up
>>>>>> + to 12 timers.
>>>>>> + Lightning Mountain has four CPUs and each CPU is configured with one GPTC
>>>>>> + timer as watchdog timer. Total four timers are configured as watchdog timers
>>>>>> + on Lightning Mountain SoC.
>>>>>> +
>>>>> Why not just one ? The watchdog subsystem does not monitor individual CPUs,
>>>>> it monitors the system.
>>>> Intel Atom based Lightning Mountain SoC, system has four CPUs. On Lightning Mountain SoC ,Watchdog subsystem is combination of GPTC timers and reset controller unit. On Lightning Mountain SoC, each CPU is configured with one GPTC timer, so that if any of the CPU hangs or freezes, the watchdog daemon running on respective CPU cannot reset/ping or pet the watchdog timer. This causes the watchdog timeout. On watchdog timeout, reset controller triggers the reset to respective CPU.
>>>>
>>> A system watchdog driver should not duplicate functionality
>>> from kernel/watchdog.c, which monitors individual CPUs.
>>> If the SoC does nto provide a system watchdog timer (which
>>> I think is unlikely), it should stick with that. A watchdog
>>> resetting an individual CPU instead of the entire system
>>> isn't something I would want to see in the watchdog subsystem.
>> My bad here, complete hardware reset happens on watchdog timeout not a single CPU or core.
>> Could you please clarify: The complete system means, you mean, "a watchdog susbsystem should monitor all the cores/cpus in the SoC. Not like each core/cpu in SoC having a wdt".
>>
> No, the watchdog subsystem does not monitor "all cores".
> Again, that is the responsibility of kernel/watchdog.c.
I am a bit confused here.
I have gone through the kernel/watchdog.c code and i see hrtimers are
used and panic is triggered for lockup on CPU/core.
It looks similar to the watchdog subsystem which uses wdt and triggers
hardware reset on timeout, whereas kernel/watchdog.c using hrtimers and
triggers panic on timeout.
To my understanding Watchdog timer recovers the hardware from software
hangs or freeze states on the CPU / cores.
Also, what does system mean in your statement " watchdog subsystem
monitors the system"? What all comes under the system other than the
cores/cpus.
And also i see there is no other watchdog subsystem in Lightning
Mountain architecture.
Regards,
Dilip
>
> Guenter
>
>> Regards,
>> Dilip
>>> Guenter
>>>
next prev parent reply other threads:[~2020-06-11 9:38 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-08 5:49 [PATCH 0/2] Driver for watchdog timer on Intel Lightning Mountain SoC Dilip Kota
2020-06-08 5:49 ` [PATCH 1/2] dt-bindings: watchdog: intel: Add YAML Schemas for Watchdog timer Dilip Kota
2020-06-08 13:37 ` Guenter Roeck
2020-06-09 8:57 ` Dilip Kota
2020-06-09 13:46 ` Guenter Roeck
2020-06-10 7:54 ` Dilip Kota
2020-06-10 13:05 ` Guenter Roeck
2020-06-11 9:38 ` Dilip Kota [this message]
2020-06-11 17:09 ` Guenter Roeck
2020-06-08 5:49 ` [PATCH 2/2] watchdog: intel: Watchdog timer support on Lightning Mountain Dilip Kota
2020-06-08 13:36 ` Guenter Roeck
2020-06-09 8:57 ` Dilip Kota
2020-06-09 13:42 ` Guenter Roeck
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4feae044-1956-fb70-7786-19c7c48cc391@linux.intel.com \
--to=eswara.kota@linux.intel.com \
--cc=andriy.shevchenko@intel.com \
--cc=cheol.yong.kim@intel.com \
--cc=devicetree@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-watchdog@vger.kernel.org \
--cc=linux@roeck-us.net \
--cc=qi-ming.wu@intel.com \
--cc=robbh@kernel.org \
--cc=wim@linux-watchdog.org \
--cc=yixin.zhu@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).