watchdog: npcm: Enable clock if provided

On the Nuvoton WPCM450 SoC, with its upcoming clock driver, peripheral
clocks are individually gated and ungated. Therefore, the watchdog
driver must be able to ungate the watchdog clock.

Signed-off-by: Jonathan Neuschäfer <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/npcm_wdt.c

···
 // Copyright (c) 2018 IBM Corp.
 
 #include <linux/bitops.h>
+#include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
···
 struct npcm_wdt {
 	struct watchdog_device  wdd;
 	void __iomem		*reg;
+	struct clk		*clk;
 };
 
 static inline struct npcm_wdt *to_npcm_wdt(struct watchdog_device *wdd)
···
 {
 	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
 	u32 val;
+
+	if (wdt->clk)
+		clk_prepare_enable(wdt->clk);
 
 	if (wdd->timeout < 2)
 		val = 0x800;
···
 	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
 
 	writel(0, wdt->reg);
+
+	if (wdt->clk)
+		clk_disable_unprepare(wdt->clk);
 
 	return 0;
 }
···
 {
 	struct npcm_wdt *wdt = to_npcm_wdt(wdd);
 
+	/* For reset, we start the WDT clock and leave it running. */
+	if (wdt->clk)
+		clk_prepare_enable(wdt->clk);
+
 	writel(NPCM_WTR | NPCM_WTRE | NPCM_WTE, wdt->reg);
 	udelay(1000);
 
···
 	wdt->reg = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(wdt->reg))
 		return PTR_ERR(wdt->reg);
+
+	wdt->clk = devm_clk_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(wdt->clk))
+		return PTR_ERR(wdt->clk);
 
 	irq = platform_get_irq(pdev, 0);
 	if (irq < 0)