Message-ID: <af9c6747-120e-48c1-8c04-9594c9b49666@tuxon.dev>
Date: Fri, 12 Apr 2024 17:02:04 +0300
From: claudiu beznea <claudiu.beznea@...on.dev>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: wim@...ux-watchdog.org, linux@...ck-us.net, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, p.zabel@...gutronix.de,
 geert+renesas@...der.be, magnus.damm@...il.com, biju.das.jz@...renesas.com,
 linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH RESEND v8 09/10] watchdog: rzg2l_wdt: Power on the PM
 domain in rzg2l_wdt_restart()

Hi, Ulf,

On 12.04.2024 14:14, Ulf Hansson wrote:
> On Wed, 10 Apr 2024 at 16:19, Claudiu <claudiu.beznea@...on.dev> wrote:
>>
>> From: Claudiu Beznea <claudiu.beznea.uj@...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@...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,
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

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