[PATCH 2/2] watchdog: msc313e: Enable clock before accessing hardware registers

[Tzung-Bi Shih <tzungbi@kernel.org>]

msc313e_wdt_probe() reads from hardware registers without ensuring the
required clock is enabled.  Furthermore, if the bootloader leaves the
watchdog running, msc313e_wdt_probe() sets WDOG_HW_RUNNING without
increasing the clock's reference count.

While the clock is currently supplied as a fixed clock by the device
tree (`xtal_div2` in arch/arm/boot/dts/sigmastar/mstar-v7.dtsi) which
masks the physical issue, this still violates the API usage.

Call clk_prepare_enable() before reading WDT registers.  If the WDT is
running, leave the clock enabled so the CCF reference counter is
balanced.

Fixes: ffd264bd152c ("watchdog: msc313e: Check if the WDT was running at boot")
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
 drivers/watchdog/msc313e_wdt.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/msc313e_wdt.c b/drivers/watchdog/msc313e_wdt.c
index f69d66971c41..b279ef645430 100644
--- a/drivers/watchdog/msc313e_wdt.c
+++ b/drivers/watchdog/msc313e_wdt.c
@@ -97,6 +97,7 @@ static int msc313e_wdt_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct msc313e_wdt_priv *priv;
+	int ret;
 
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -119,9 +120,21 @@ static int msc313e_wdt_probe(struct platform_device *pdev)
 	priv->wdev.max_timeout = U32_MAX / clk_get_rate(priv->clk);
 	priv->wdev.timeout = MSC313E_WDT_DEFAULT_TIMEOUT;
 
+	ret = clk_prepare_enable(priv->clk);
+	if (ret)
+		return ret;
+
 	/* If the period is non-zero the WDT is running */
-	if (readw(priv->base + REG_WDT_MAX_PRD_L) | (readw(priv->base + REG_WDT_MAX_PRD_H) << 16))
+	if (readw(priv->base + REG_WDT_MAX_PRD_L) | (readw(priv->base + REG_WDT_MAX_PRD_H) << 16)) {
 		set_bit(WDOG_HW_RUNNING, &priv->wdev.status);
+		/*
+		 * Keep the clock enabled. The watchdog core will skip the next
+		 * start() and a future stop() will balance the CCF reference
+		 * count.
+		 */
+	} else {
+		clk_disable_unprepare(priv->clk);
+	}
 
 	watchdog_set_drvdata(&priv->wdev, priv);
 	platform_set_drvdata(pdev, priv);
-- 
2.55.0.887.g758fc8c411-goog