Re: [PATCH RESEND v8 09/10] watchdog: rzg2l_wdt: Power on the PM domain in rzg2l_wdt_restart()

[claudiu beznea <claudiu.beznea@tuxon.dev>]

Hi, Ulf,

On 12.04.2024 17:02, claudiu beznea wrote:
> Hi, Ulf,
> 
> On 12.04.2024 14:14, Ulf Hansson wrote:
>> On Wed, 10 Apr 2024 at 16:19, Claudiu <claudiu.beznea@tuxon.dev> wrote:
>>>
>>> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>>
>>> The rzg2l_wdt_restart() is called from atomic context. Calling
>>> pm_runtime_{get_sync, resume_and_get}() or any other runtime PM resume
>>> APIs is not an option as it may lead to issues as described in commit
>>> e4cf89596c1f ("watchdog: rzg2l_wdt: Fix 'BUG: Invalid wait context'")
>>> that removed the pm_runtime_get_sync() and used directly the
>>> clk_prepare_enable() APIs.
>>>
>>> Starting with RZ/G3S the watchdog could be part of its own software
>>> controlled power domain (see the initial implementation in Link section).
>>> In case the watchdog is not used the power domain is off and accessing
>>> watchdog registers leads to aborts.
>>>
>>> To solve this the patch powers on the power domain using
>>> dev_pm_genpd_resume() API before enabling its clock. This is not
>>> sleeping or taking any other locks as the power domain will not be
>>> registered with GENPD_FLAG_IRQ_SAFE flags.
>>>
>>> Link: https://lore.kernel.org/all/20240208124300.2740313-1-claudiu.beznea.uj@bp.renesas.com
>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>> ---
>>>
>>> Changes in v8:
>>> - none, this patch is new
>>>
>>>  drivers/watchdog/rzg2l_wdt.c | 12 ++++++++++++
>>>  1 file changed, 12 insertions(+)
>>>
>>> diff --git a/drivers/watchdog/rzg2l_wdt.c b/drivers/watchdog/rzg2l_wdt.c
>>> index c8c20cfb97a3..98e5e9914a5d 100644
>>> --- a/drivers/watchdog/rzg2l_wdt.c
>>> +++ b/drivers/watchdog/rzg2l_wdt.c
>>> @@ -12,6 +12,7 @@
>>>  #include <linux/module.h>
>>>  #include <linux/of.h>
>>>  #include <linux/platform_device.h>
>>> +#include <linux/pm_domain.h>
>>>  #include <linux/pm_runtime.h>
>>>  #include <linux/reset.h>
>>>  #include <linux/units.h>
>>> @@ -164,6 +165,17 @@ static int rzg2l_wdt_restart(struct watchdog_device *wdev,
>>>         struct rzg2l_wdt_priv *priv = watchdog_get_drvdata(wdev);
>>>         int ret;
>>>
>>> +       /*
>>> +        * The device may be part of a power domain that is currently
>>> +        * powered off. We need to power it up before accessing registers.
>>> +        * We don't undo the dev_pm_genpd_resume() as the device need to
>>> +        * be up for the reboot to happen. Also, as we are in atomic context
>>> +        * here there is no need to increment PM runtime usage counter
>>> +        * (to make sure pm_runtime_active() doesn't return wrong code).
>>> +        */
>>> +       if (!pm_runtime_active(wdev->parent))
>>> +               dev_pm_genpd_resume(wdev->parent);
>>> +
>>
>> I doubt this is the correct solution, but I may be wrong. Unless this
>> is invoked at the syscore stage?
> 
> On my case I see it invoked from kernel_restart(). As of my code reading,

With the above explanations, do you consider calling dev_pm_genpd_resume()
here is still wrong?

Do you have any suggestions I could try?

Thank you,
Claudiu Beznea

> at that point only one CPU is active with IRQs disabled (done in
> machine_restart()). Below is the stack trace decoded on next-20240410 with
> this series
> (https://lore.kernel.org/all/20240410134044.2138310-1-claudiu.beznea.uj@bp.renesas.com/)
> on top and the one from here (adding power domain support):
> https://lore.kernel.org/all/20240410122657.2051132-1-claudiu.beznea.uj@bp.renesas.com/
> 
> Hardware name: Renesas SMARC EVK version 2 based on r9a08g045s33 (DT)
> Call trace:
> dump_backtrace (arch/arm64/kernel/stacktrace.c:319)
> show_stack (arch/arm64/kernel/stacktrace.c:326)
> dump_stack_lvl (lib/dump_stack.c:117)
> dump_stack (lib/dump_stack.c:124)
> rzg2l_wdt_restart (drivers/watchdog/rzg2l_wdt.c:180)
> watchdog_restart_notifier (drivers/watchdog/watchdog_core.c:188)
> atomic_notifier_call_chain (kernel/notifier.c:98 kernel/notifier.c:231)
> do_kernel_restart (kernel/reboot.c:236)
> machine_restart (arch/arm64/kernel/process.c:145)
> kernel_restart (kernel/reboot.c:287)
> __do_sys_reboot (kernel/reboot.c:755)
> __arm64_sys_reboot (kernel/reboot.c:715)
> invoke_syscall (arch/arm64/include/asm/current.h:19
> arch/arm64/kernel/syscall.c:53)
> el0_svc_common.constprop.0 (include/linux/thread_info.h:127
> arch/arm64/kernel/syscall.c:141)
> do_el0_svc (arch/arm64/kernel/syscall.c:153)
> el0_svc (arch/arm64/include/asm/irqflags.h:56
> arch/arm64/include/asm/irqflags.h:77 arch/arm64/kernel/entry-common.c:165
> arch/arm64/kernel/entry-common.c:178 arch/arm64/kernel/entry-common.c:713)
> el0t_64_sync_handler (arch/arm64/kernel/entry-common.c:731)
> el0t_64_sync (arch/arm64/kernel/entry.S:598)
> 
> The watchdog restart handler is added in restart_handler_list and this list
> is invoked though do_kernel_restart(). As of my code investigation the
> restart_handler_list is invoked only though do_kernel_restart() and only
> though the stack trace above.
> 
> Thank you,
> Claudiu Beznea
> 
>>
>>>         clk_prepare_enable(priv->pclk);
>>>         clk_prepare_enable(priv->osc_clk);
>>>
>>> --
>>> 2.39.2
>>>
>>>
>>
>> Can you redirectly me to the complete series, so I can have a better
>> overview of the problem?
> 
> This is the series that adds power domain support for RZ/G3S SoC:
> https://lore.kernel.org/all/20240410122657.2051132-1-claudiu.beznea.uj@bp.renesas.com/
> 
> This is the series that adds watchdog support for RZ/G3S SoC:
> https://lore.kernel.org/all/20240410134044.2138310-1-claudiu.beznea.uj@bp.renesas.com/
> 
> Thank you for your review,
> Claudiu Beznea
> 
>>
>> Kind regards
>> Uffe