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

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

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);
+
 	clk_prepare_enable(priv->pclk);
 	clk_prepare_enable(priv->osc_clk);
 
-- 
2.39.2