linux-kernel - [PATCH RFC 0/3] watchdog: rzg2l_wdt: Enable properly the watchdog clocks and power domain

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Date: Wed, 19 Jun 2024 15:09:17 +0300
From: Claudiu <claudiu.beznea@...on.dev>
To: ulf.hansson@...aro.org,
	wim@...ux-watchdog.org,
	linux@...ck-us.net,
	rafael@...nel.org
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-watchdog@...r.kernel.org,
	claudiu.beznea@...on.dev,
	geert+renesas@...der.be,
	linux-renesas-soc@...r.kernel.org,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: [PATCH RFC 0/3] watchdog: rzg2l_wdt: Enable properly the watchdog clocks and power domain

From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

Hi,

Watchdog device available on RZ/G3S SoC is part of a software-controlled
power domain. The watchdog driver implements struct
watchdog_ops::restart() handler which is called in atomic context via
this call chain:

kernel_restart() ->
  machine_restart() ->
    do_kernel_restart() ->
      atomic_notifier_call_chain() ->
        watchdog_restart_notifier()
	  rzg2l_wdt_restart()

When the rzg2l_wdt_restart() is called it may happen that the watchdog
clocks to be disabled and the associated power domain to be off.
Accessing watchdog registers in this state leads to aborts and system
blocks.

To solve this issue the series proposes a new API called
dev_pm_genpd_resume_restart_dev() that is intended to be called in
scenarios like this. In this RFC series the
dev_pm_genpd_resume_restart_dev() checks if the system is in
SYSTEM_RESTART context and call dev_pm_genpd_resume(). I also wanted to
mark the device as a restart device with a new member in struct dev_pm_info
(similar to struct dev_pm_info::syscore) and check it in the newly
introduced API but then I told myself maybe it would be better to keep it
simpler for the moment.

Please let me know how do you consider this.

Along with it, series addresses the usage of clk_prepare_enable() in
rzg2l_wdt_restart() reported by Ulf Hansson at [1] and use the
dev_pm_genpd_resume_restart_dev() in rzg2l_wdt driver.

Please note that series is built on top of [1].

A similar approach (using directly the dev_pm_genpd_resume() function in
rzg2l_wdt was proposed at [2]). This series was posted separatelly to
avoid blocking the initial support for the RZ/G3S SoC.

Thank you,
Claudiu Beznea

[1] https://lore.kernel.org/all/20240531065723.1085423-1-claudiu.beznea.uj@bp.renesas.com/
[2] https://lore.kernel.org/all/20240410134044.2138310-10-claudiu.beznea.uj@bp.renesas.com/

Claudiu Beznea (3):
  pmdomain: core: Add a helper to power on the restart devices
  watchdog: rzg2l_wdt: Keep the clocks prepared
  watchdog: rzg2l_wdt: Power on the PM domain in rzg2l_wdt_restart()

 drivers/pmdomain/core.c      | 18 +++++++++++++++
 drivers/watchdog/rzg2l_wdt.c | 43 +++++++++++++++++++++++++++++++-----
 include/linux/pm_domain.h    |  2 ++
 3 files changed, 58 insertions(+), 5 deletions(-)

-- 
2.39.2