[PATCH v3 0/6] Improved sysreset/watchdog uclass integration

Heinrich Schuchardt heinrich.schuchardt at canonical.com
Sun Nov 7 12:18:44 CET 2021

On 11/6/21 14:53, Tom Rini wrote:
> On Sat, Nov 06, 2021 at 04:55:44AM +0100, Heinrich Schuchardt wrote:
>> On 11/6/21 02:52, Andre Przywara wrote:
>>> On Fri, 5 Nov 2021 18:56:34 -0400
>>> Tom Rini <trini at konsulko.com> wrote:
>>>> On Fri, Nov 05, 2021 at 09:38:50PM +0100, Heinrich Schuchardt wrote:
>>>>> On 11/5/21 20:17, Tom Rini wrote:
>>>>>> On Fri, Nov 05, 2021 at 07:37:02PM +0100, Heinrich Schuchardt wrote:
>>>>>>> On 11/5/21 17:12, Simon Glass wrote:
>>>>>>>> Hi,
>>>>>>>> On Fri, 5 Nov 2021 at 08:21, Tom Rini <trini at konsulko.com> wrote:
>>>>>>>>> On Fri, Nov 05, 2021 at 12:14:47PM +0100, Stefan Roese wrote:
>>>>>>>>>> Hi Andre,
>>>>>>>>>> Added Tom to Cc.
>>>>>>>>>> On 05.11.21 11:04, Andre Przywara wrote:
>>>>>>>>>>> On Thu, 4 Nov 2021 20:02:41 -0600
>>>>>>>>>>> Simon Glass <sjg at chromium.org> wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>>> On Thu, 4 Nov 2021 at 19:22, Stefan Roese <sr at denx.de> wrote:
>>>>>>>>>>>>> Hi Andre,
>>>>>>>>>>>>> On 05.11.21 00:11, Andre Przywara wrote:
>>>>>>>>>>>>>> On Thu, 4 Nov 2021 11:37:57 +0100
>>>>>>>>>>>>>> Stefan Roese <sr at denx.de> wrote:
>>>>>>>>>>>>>> Hi Stefan,
>>>>>>>>>>>>>>> On 04.11.21 04:55, Samuel Holland wrote:
>>>>>>>>>>>>>>>> This series hooks up the watchdog uclass to automatically register
>>>>>>>>>>>>>>>> watchdog devices for use with sysreset, doing a bit of minor cleanup
>>>>>>>>>>>>>>>> along the way.
>>>>>>>>>>>>>>>> The goal is for this to replace the sunxi board-level non-DM reset_cpu()
>>>>>>>>>>>>>>>> function. I was surprised to find that the wdt_reboot driver requires
>>>>>>>>>>>>>>>> its own undocumented device tree node, which references the watchdog
>>>>>>>>>>>>>>>> device by phandle. This is problematic for us, because sunxi-u-boot.dtsi
>>>>>>>>>>>>>>>> file covers 20 different SoCs with varying watchdog node phandle names.
>>>>>>>>>>>>>>>> So it would have required adding a -u-boot.dtsi file for each board.
>>>>>>>>>>>>>>>> Hooking things up automatically makes sense to me; this is what Linux
>>>>>>>>>>>>>>>> does. However, I put the code behind a new option to avoid surprises for
>>>>>>>>>>>>>>>> other platforms.
>>>>>>>>>>>>>>>> Changes in v3:
>>>>>>>>>>>>>>>>         - Move condition to wdt-uclass.c to fix build errors.
>>>>>>>>>>>>>>>>         - Include watchdog name in error message.
>>>>>>>>>>>>>>>> Changes in v2:
>>>>>>>>>>>>>>>>         - Extend the "if SYSRESET" block to the end of the file.
>>>>>>>>>>>>>>>>         - Also make gpio_reboot_probe function static.
>>>>>>>>>>>>>>>>         - Rebase on top of 492ee6b8d0e7 (now handle all watchdogs).
>>>>>>>>>>>>>>>>         - Added patches 5-6 as an example of how the new option will be used.
>>>>>>>>>>>>>>>> Samuel Holland (6):
>>>>>>>>>>>>>>>>          sysreset: Add uclass Kconfig dependency to drivers
>>>>>>>>>>>>>>>>          sysreset: Mark driver probe functions as static
>>>>>>>>>>>>>>>>          sysreset: watchdog: Move watchdog reference to plat data
>>>>>>>>>>>>>>>>          watchdog: Automatically register device with sysreset
>>>>>>>>>>>>>>>>          sunxi: Avoid duplicate reset_cpu with SYSRESET enabled
>>>>>>>>>>>>>>>>          sunxi: Use sysreset framework for poweroff/reset
>>>>>>>>>>>>>>>>         arch/arm/Kconfig                     |  3 +++
>>>>>>>>>>>>>>>>         arch/arm/mach-sunxi/board.c          |  2 ++
>>>>>>>>>>>>>>>>         drivers/sysreset/Kconfig             | 11 ++++++--
>>>>>>>>>>>>>>>>         drivers/sysreset/sysreset_gpio.c     |  2 +-
>>>>>>>>>>>>>>>>         drivers/sysreset/sysreset_resetctl.c |  2 +-
>>>>>>>>>>>>>>>>         drivers/sysreset/sysreset_syscon.c   |  2 +-
>>>>>>>>>>>>>>>>         drivers/sysreset/sysreset_watchdog.c | 40 ++++++++++++++++++++++------
>>>>>>>>>>>>>>>>         drivers/watchdog/wdt-uclass.c        |  8 ++++++
>>>>>>>>>>>>>>>>         include/sysreset.h                   | 10 +++++++
>>>>>>>>>>>>>>>>         9 files changed, 67 insertions(+), 13 deletions(-)
>>>>>>>>>>>>>>> Applied to u-boot-marvell
>>>>>>>>>>>>>> Mmmh, why u-boot-marvell,
>>>>>>>>>>>>> Because I'm handling watchdog related changed since a few years and we
>>>>>>>>>>>>> did not create a specific subsystem repo for this and I'm usually
>>>>>>>>>>>>> using my "marvell" one for this.
>>>>>>>>> And fwiw, there's a few other cases like this.  If it's too confusing,
>>>>>>>>> maybe we should just roll out a few more repositories, I think it's
>>>>>>>>> easier to do that now than pre-gitlab?
>>>>>>>>>>>>>> and why did this end up already in master?
>>>>>>>>>>>>>> Isn't that material for the next merge window? After all this changes
>>>>>>>>>>>>>> quite a bit, for a lot of boards, and I did not have a closer look at
>>>>>>>>>>>>>> the sunxi parts yet.
>>>>>>>>>>>>> I was hesitating also a bit. But since this patchset is on the list in
>>>>>>>>>>>>> v1 since over 2 months now (2021-08-21) I thought it was "ready" for
>>>>>>>>>>>>> inclusion now. We are at -rc1 and I think we still have enough time to
>>>>>>>>>>>>> fix any resulting problems in this release cycle.
>>>>>>>>>>> Why do we have the merge window then? This is clearly not a regression or
>>>>>>>>>>> general fix.
>>>>>>>>>> AFAIU, we are a bit less strict here in U-Boot. Patches that were posted
>>>>>>>>>> before the merge-window and skipped the review process (most likely
>>>>>>>>>> because of lack of time) are often still integrated in the early rcX
>>>>>>>>>> cycles. At least this is how I handle it usually.
>>>>>>>>>> Tom, is my understanding here correct?
>>>>>>>>> Yes.  We are not as strict as the kernel is about what can come in
>>>>>>>>> between rc1 and rc2 (and to a certain degree, post rc2).  I leave things
>>>>>>>>> up to the discretion of the custodians.  People tend of have less time
>>>>>>>>> to handle U-Boot changes than other stuff, so I try and be flexible in
>>>>>>>>> picking things up.
>>>>>>>>>>>> Yes I agree, that should be plenty of time for people to review it.
>>>>>>>>>>> Well, if there would be people to review the sunxi parts :-(
>>>>>>>>>>> I am totally fine with the generic patches (as they have been reviewed),
>>>>>>>>>>> but the sunxi integration is somewhat risky.
>>>>>>>>>>> I was explicitly deprioritising that in my queue, as it really doesn't
>>>>>>>>>>> change, add or fix anything, it's mere refactoring, from the user's point
>>>>>>>>>>> of view.
>>>>>>>>>>>>> Do you see any specific issues?
>>>>>>>>>>> Patch 6/6 changes the config for all 157 Allwinner boards, so I think that
>>>>>>>>>>> deserves at least some testing, *before* merging it.
>>>>>>>>>> I expect that Samuel did some testing. But still, I agree that it
>>>>>>>>>> would be much better, if these patches - especially the Allwinner parts
>>>>>>>>>> got more extensive testing.
>>>>>>>>>>> I will do as much testing now as possible, but I am not happy about that
>>>>>>>>>>> situation.
>>>>>>>>>> Understood. Should we revert patch 6/6 for now?
>>>>>>>>> FWIW, given Samuel has been doing a number of allwinner changes, I had
>>>>>>>>> also assumed it was sufficiently tested, which is why I didn't raise a
>>>>>>>>> further concern when I saw the widespread nature of the overall changes,
>>>>>>>>> just figured it was a few more ready-to-go cleanups that weren't quite
>>>>>>>>> picked up in time.  Please do speak up if you want me to revert the last
>>>>>>>>> part.
>>>>>>>> Also it is often true that people find problems by testing on master
>>>>>>>> so applying it helps to shake the tree a bit.
>>>>>>>> Regards,
>>>>>>>> Simon
>>>>>>> We don't actually have a problem with this series but with a previous
>>>>>>> watchdog patch. The culprit according to bisecting is:
>>>>>>> b147bd3607f8 ("sunxi: Enable watchdog timer support by default")
>>>>>>> When booting the OrangePi PC the watchdog triggers while Linux is booting,
>>>>>>> ca. 16 s after leaving the UEFI subsystem. This matches WDT_MAX_TIMEOUT in
>>>>>>> drivers/watchdog/sunxi_wdt.c.
>>>>>>> If I run
>>>>>>> => wdt dev watchdog at 1c20ca0
>>>>>>> => wdt stop
>>>>>>> before the bootefi command booting succeeds.
>>>>>>> We don't disarm the watchdog and Linux does not do it for us in time.
>>>>>>> The UEFI specification requires that the default watchdog reset time is 300
>>>>>>> s. We should never arm the Sunxi hardware watchdog except within the
>>>>>>> watchdog reset driver.
>>>>>>> The solution is to disable CONFIG_WATCHDOG_AUTOSTART on SUNXI. See
>>>>>>> [PATCH 1/1] watchdog: don't autostart watchdog on Sunxi boards
>>>>>>> https://lists.denx.de/pipermail/u-boot/2021-November/466318.html
>>>>>> This means we never did come up with a satisfactory to everyone solution
>>>>>> to what UEFI thinks a watchdog should do, and what other types of
>>>>>> deployment think a watchdog should do, yes?
>>>>> Dear Tom,
>>>>> The issue is *not* UEFI specific.
>>>>> A watchdog timeout of 16 seconds is too short for Linux to boot no matter
>>>>> whether you use the EFI stub or the legacy entry point.
>>>>> I only referred to the UEFI specification as it indicates what can be
>>>>> considered as a reasonable timeout interval: 300 seconds.
>>>> 16 seconds from the last time we pet the watchdog in U-Boot to the
>>>> kernel being able to take over is quite reasonable.
>>> How do we know that the kernel takes over? What if the kernel/EFI
>>> payload doesn't have a watchdog driver? I was assuming that the
>>> watchdog would be disabled as soon as we boot a kernel or an EFI app
>>> calls ExitBootServices (maybe even earlier).
>>> But this sounds like a generic problem, not sunxi specific. So how do
>>> other platforms solve this?
>>> Cheers,
>>> Andre
>> The UEFI specification has this requirement in chapter "3.1.2 Load Option
>> Processing":
>> "... the boot manager must enable the watchdog timer for 5 minutes by using
>> the EFI_BOOT_SERVICES.SetWatchdogTimer() boot service prior to calling
>> EFI_BOOT_SERVICES.StartImage(). If a boot option returns control to the boot
>> manager, the boot manager must disable the watchdog timer with an additional
>> call to the SetWatchdogTimer() boot service."
>> This means that having an armed watchdog when starting the kernel is
>> correct.
>> If you start a watchdog in the firmware which is not disabled or reset by
>> the operating system, you are out of luck and won't be able to boot.
>> Current Linux has driver drivers/watchdog/sunxi_wdt.c compatible to
>> "allwinner,sun4i-a10-wdt","allwinner,sun6i-a31-wdt" and enabled by
>> CONFIG_SUNXI_WATCHDOG. This driver was introduced in Linux v3.12. It
>> originally had compatible "allwinner,sun4i-wdt" only.
>> Debian Bullseye has the driver enabled as a module. In the bootlog of the
>> Orange Pi PC I find:
>> [   12.321909] sunxi-wdt 1c20ca0.watchdog: Watchdog enabled (timeout=16 sec,
>> nowayout=0)
>> This message appears approximately *20 seconds* after the EFI stub hands
>> over to the main kernel. Adding the driver to initrd shortens this to *18
>> seconds*. The message occurs after file system checks which can be a lengthy
>> operation. In Debian systemd manages the watchdog.
>> As I said: 16 seconds is way too short for a hardware watchdog timeout.
> What's the time if you build it in?

For sure you will find some board and configuration that is faster.

But why should I care? This series breaks booting Debian on my board. So 
it needs to be fixed. So, please, apply my patch that is doing so.

Best regards


More information about the U-Boot mailing list