Linux-Watchdog Archive on
 help / color / Atom feed
From: Guenter Roeck <>
To: Ken Sloat <>
Cc: "" <>,
	"" <>,
	"" <>,
	"" <>
Subject: Re: [RFE]: watchdog: atmel: atmel-sama5d4-wdt
Date: Mon, 10 Jun 2019 09:28:11 -0700
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, Jun 10, 2019 at 03:51:52PM +0000, Ken Sloat wrote:
> Hello Nicolas,
> I wanted to open a discussion proposing new functionality to allow disabling of the watchdog timer upon entering 
> suspend in the SAMA5D2/4.
> Typical use case of a hardware watchdog timer in the kernel is a userspace application opens the watchdog timer and
> periodically "kicks" it. If the application hits a deadlock somewhere and is no longer able to kick it, then the watchdog
> intervenes and often resets the processor. Such is the case for the Atmel driver (which also allows a watchdog interrupt
> to be asserted in lieu of a system reset). In most use cases, upon entering a low power/suspend state, the application 
> will no longer be able to "kick" the watchdog. If the watchdog is not disabled or kicked via another method, then it will
> reset the system. This is the current behavior of the Atmel driver as of today.
> The watchdog peripheral itself does have a "WDIDLEHLT" bit however, and this is enabled via the "atmel,idle-halt" dt
> property. However, this is not very useful, as it literally only makes the watchdog count when the CPU is active. This 
> results in non-deterministic triggering of the WDT and means that if a critical application were to crash, it may be
> quite a long time before the WDT would ever trigger. Below is a similar statement made in the device-tree doc for this
> peripheral:
> - atmel,idle-halt: present if you want to stop the watchdog when the CPU is
> 		   in idle state.
> 	CAUTION: This property should be used with care, it actually makes the
> 	watchdog not counting when the CPU is in idle state, therefore the
> 	watchdog reset time depends on mean CPU usage and will not reset at all
> 	if the CPU stop working while it is in idle state, which is probably
> 	not what you want.
> It seems to me, that it would be logical and useful to introduce a new property that would cause the Atmel WDT
> to disable on suspend and re-enable on resume. It also appears that the WDT is re-initialized anyways upon
> resume, so the only piece missing here would really be a dt flag and a call to disable.
Wondering - why would this need a dt property ? That would be quite unusual. Is
there a condition where one would _not_ want the watchdog to stop on suspend ?

If anything I would suggest to drop atmel,idle-halt completely; it really looks
like it would make the watchdog unreliable.


  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10 15:51 Ken Sloat
2019-06-10 16:28 ` Guenter Roeck [this message]
2019-06-10 17:40   ` Ken Sloat
2019-06-10 20:13   ` Alexandre Belloni
2019-06-10 20:29     ` Guenter Roeck
2019-06-10 20:52       ` Ken Sloat

Reply instructions:

You may reply publically 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:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Watchdog Archive on

Archives are clonable:
	git clone --mirror linux-watchdog/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-watchdog linux-watchdog/ \
	public-inbox-index linux-watchdog

Newsgroup available over NNTP:

AGPL code for this site: git clone public-inbox