watchdog: jz4740: Use WDT clock provided by TCU driver

Instead of requesting the "ext" clock and handling the watchdog clock
divider and gating in the watchdog driver, we now request and use the
"wdt" clock that is supplied by the ingenic-timer "TCU" driver.

The major benefit is that the watchdog's clock rate and parent can now
be specified from within devicetree, instead of hardcoded in the driver.

Also, this driver won't poke anymore into the TCU registers to
enable/disable the clock, as this is now handled by the TCU driver.

On the bad side, we break the ABI with devicetree - as we now request a
different clock. In this very specific case it is still okay, as every
Ingenic JZ47xx-based board out there compile the devicetree within the
kernel; so it's still time to push breaking changes, in order to get a
clean devicetree that won't break once it musn't.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: Mathieu Malaterre <malat@debian.org>
Tested-by: Artur Rojek <contact@artur-rojek.eu>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20191023174714.14362-1-paul@crapouillou.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/Kconfig

@@ -1643,6 +1643,7 @@ config INDYDOG
 config JZ4740_WDT
 	tristate "Ingenic jz4740 SoC hardware watchdog"
 	depends on MACH_JZ4740 || MACH_JZ4780
+	depends on COMMON_CLK
 	select WATCHDOG_CORE
 	help
 	  Hardware driver for the built-in watchdog timer on Ingenic jz4740 SoCs.

drivers/watchdog/jz4740_wdt.c

@@ -18,19 +18,6 @@
 #include <linux/err.h>
 #include <linux/of.h>
 
-#include <asm/mach-jz4740/timer.h>
-
-#define JZ_WDT_CLOCK_PCLK 0x1
-#define JZ_WDT_CLOCK_RTC  0x2
-#define JZ_WDT_CLOCK_EXT  0x4
-
-#define JZ_WDT_CLOCK_DIV_1    (0 << TCU_TCSR_PRESCALE_LSB)
-#define JZ_WDT_CLOCK_DIV_4    (1 << TCU_TCSR_PRESCALE_LSB)
-#define JZ_WDT_CLOCK_DIV_16   (2 << TCU_TCSR_PRESCALE_LSB)
-#define JZ_WDT_CLOCK_DIV_64   (3 << TCU_TCSR_PRESCALE_LSB)
-#define JZ_WDT_CLOCK_DIV_256  (4 << TCU_TCSR_PRESCALE_LSB)
-#define JZ_WDT_CLOCK_DIV_1024 (5 << TCU_TCSR_PRESCALE_LSB)
-
 #define DEFAULT_HEARTBEAT 5
 #define MAX_HEARTBEAT     2048
 
@@ -50,7 +37,8 @@ MODULE_PARM_DESC(heartbeat,
 struct jz4740_wdt_drvdata {
 	struct watchdog_device wdt;
 	void __iomem *base;
-	struct clk *rtc_clk;
+	struct clk *clk;
+	unsigned long clk_rate;
 };
 
 static int jz4740_wdt_ping(struct watchdog_device *wdt_dev)
@@ -65,32 +53,14 @@ static int jz4740_wdt_set_timeout(struct watchdog_device *wdt_dev,
 				    unsigned int new_timeout)
 {
 	struct jz4740_wdt_drvdata *drvdata = watchdog_get_drvdata(wdt_dev);
-	unsigned int rtc_clk_rate;
-	unsigned int timeout_value;
-	unsigned short clock_div = JZ_WDT_CLOCK_DIV_1;
+	u16 timeout_value = (u16)(drvdata->clk_rate * new_timeout);
 	u8 tcer;
 
-	rtc_clk_rate = clk_get_rate(drvdata->rtc_clk);
-
-	timeout_value = rtc_clk_rate * new_timeout;
-	while (timeout_value > 0xffff) {
-		if (clock_div == JZ_WDT_CLOCK_DIV_1024) {
-			/* Requested timeout too high;
-			* use highest possible value. */
-			timeout_value = 0xffff;
-			break;
-		}
-		timeout_value >>= 2;
-		clock_div += (1 << TCU_TCSR_PRESCALE_LSB);
-	}
-
 	tcer = readb(drvdata->base + TCU_REG_WDT_TCER);
 	writeb(0x0, drvdata->base + TCU_REG_WDT_TCER);
-	writew(clock_div, drvdata->base + TCU_REG_WDT_TCSR);
 
 	writew((u16)timeout_value, drvdata->base + TCU_REG_WDT_TDR);
 	writew(0x0, drvdata->base + TCU_REG_WDT_TCNT);
-	writew(clock_div | JZ_WDT_CLOCK_RTC, drvdata->base + TCU_REG_WDT_TCSR);
 
 	if (tcer & TCU_WDT_TCER_TCEN)
 		writeb(TCU_WDT_TCER_TCEN, drvdata->base + TCU_REG_WDT_TCER);
@@ -102,11 +72,15 @@ static int jz4740_wdt_set_timeout(struct watchdog_device *wdt_dev,
 static int jz4740_wdt_start(struct watchdog_device *wdt_dev)
 {
 	struct jz4740_wdt_drvdata *drvdata = watchdog_get_drvdata(wdt_dev);
+	int ret;
 	u8 tcer;
 
+	ret = clk_prepare_enable(drvdata->clk);
+	if (ret)
+		return ret;
+
 	tcer = readb(drvdata->base + TCU_REG_WDT_TCER);
 
-	jz4740_timer_enable_watchdog();
 	jz4740_wdt_set_timeout(wdt_dev, wdt_dev->timeout);
 
 	/* Start watchdog if it wasn't started already */
@@ -121,7 +95,7 @@ static int jz4740_wdt_stop(struct watchdog_device *wdt_dev)
 	struct jz4740_wdt_drvdata *drvdata = watchdog_get_drvdata(wdt_dev);
 
 	writeb(0x0, drvdata->base + TCU_REG_WDT_TCER);
-	jz4740_timer_disable_watchdog();
+	clk_disable_unprepare(drvdata->clk);
 
 	return 0;
 }
@@ -162,21 +136,38 @@ static int jz4740_wdt_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct jz4740_wdt_drvdata *drvdata;
 	struct watchdog_device *jz4740_wdt;
+	long rate;
+	int ret;
 
 	drvdata = devm_kzalloc(dev, sizeof(struct jz4740_wdt_drvdata),
 			       GFP_KERNEL);
 	if (!drvdata)
 		return -ENOMEM;
 
-	if (heartbeat < 1 || heartbeat > MAX_HEARTBEAT)
-		heartbeat = DEFAULT_HEARTBEAT;
+	drvdata->clk = devm_clk_get(&pdev->dev, "wdt");
+	if (IS_ERR(drvdata->clk)) {
+		dev_err(&pdev->dev, "cannot find WDT clock\n");
+		return PTR_ERR(drvdata->clk);
+	}
 
+	/* Set smallest clock possible */
+	rate = clk_round_rate(drvdata->clk, 1);
+	if (rate < 0)
+		return rate;
+
+	ret = clk_set_rate(drvdata->clk, rate);
+	if (ret)
+		return ret;
+
+	drvdata->clk_rate = rate;
 	jz4740_wdt = &drvdata->wdt;
 	jz4740_wdt->info = &jz4740_wdt_info;
 	jz4740_wdt->ops = &jz4740_wdt_ops;
-	jz4740_wdt->timeout = heartbeat;
 	jz4740_wdt->min_timeout = 1;
-	jz4740_wdt->max_timeout = MAX_HEARTBEAT;
+	jz4740_wdt->max_timeout = 0xffff / rate;
+	jz4740_wdt->timeout = clamp(heartbeat,
+				    jz4740_wdt->min_timeout,
+				    jz4740_wdt->max_timeout);
 	jz4740_wdt->parent = dev;
 	watchdog_set_nowayout(jz4740_wdt, nowayout);
 	watchdog_set_drvdata(jz4740_wdt, drvdata);
@@ -185,12 +176,6 @@ static int jz4740_wdt_probe(struct platform_device *pdev)
 	if (IS_ERR(drvdata->base))
 		return PTR_ERR(drvdata->base);
 
-	drvdata->rtc_clk = devm_clk_get(dev, "rtc");
-	if (IS_ERR(drvdata->rtc_clk)) {
-		dev_err(dev, "cannot find RTC clock\n");
-		return PTR_ERR(drvdata->rtc_clk);
-	}
-
 	return devm_watchdog_register_device(dev, &drvdata->wdt);
 }