watchdog: dw_wdt: Support devices with non-fixed TOP values

In case if the DW Watchdog IP core is synthesised with
WDT_USE_FIX_TOP == false, the TOP interval indexes make the device
to load a custom periods to the counter. These periods are hardwired
at the IP synthesis stage and can be within [2^8, 2^(WDT_CNT_WIDTH - 1)].
Alas their values can't be detected at runtime and must be somehow
supplied to the driver so one could properly determine the watchdog
timeout intervals. For this purpose we suggest to have a vendor-
specific dts property "snps,watchdog-tops" utilized, which would
provide an array of sixteen counter values. At device probe stage they
will be used to initialize the watchdog device timeouts determined
from the array values and current clocks source rate.

In order to have custom TOP values supported the driver must be
altered in the following way. First of all the fixed-top values
ready-to-use array must be determined for compatibility with currently
supported devices, which were synthesised with WDT_USE_FIX_TOP == true.
It will be used if either fixed TOP feature is detected being enabled or
no custom TOPs are fetched from the device dt node. Secondly at the probe
stage we must initialize an array of the watchdog timeouts corresponding
to the detected TOPs list and the reference clock rate. For generality the
procedure of initialization is designed in a way to support the TOPs array
with no limitations on the items order or value. Finally the watchdog
period search methods should be altered to support the new timeouts data
structure.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org
Link: https://lore.kernel.org/r/20200530073557.22661-5-Sergey.Semin@baikalelectronics.ruSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/dw_wdt.c

@@ -13,6 +13,8 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/limits.h>
+#include <linux/kernel.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/err.h>
@@ -34,21 +36,40 @@
 #define WDOG_CURRENT_COUNT_REG_OFFSET	    0x08
 #define WDOG_COUNTER_RESTART_REG_OFFSET     0x0c
 #define WDOG_COUNTER_RESTART_KICK_VALUE	    0x76
+#define WDOG_COMP_PARAMS_1_REG_OFFSET       0xf4
+#define WDOG_COMP_PARAMS_1_USE_FIX_TOP      BIT(6)
 
-/* The maximum TOP (timeout period) value that can be set in the watchdog. */
-#define DW_WDT_MAX_TOP		15
+/* There are sixteen TOPs (timeout periods) that can be set in the watchdog. */
+#define DW_WDT_NUM_TOPS		16
+#define DW_WDT_FIX_TOP(_idx)	(1U << (16 + _idx))
 
 #define DW_WDT_DEFAULT_SECONDS	30
 
+static const u32 dw_wdt_fix_tops[DW_WDT_NUM_TOPS] = {
+	DW_WDT_FIX_TOP(0), DW_WDT_FIX_TOP(1), DW_WDT_FIX_TOP(2),
+	DW_WDT_FIX_TOP(3), DW_WDT_FIX_TOP(4), DW_WDT_FIX_TOP(5),
+	DW_WDT_FIX_TOP(6), DW_WDT_FIX_TOP(7), DW_WDT_FIX_TOP(8),
+	DW_WDT_FIX_TOP(9), DW_WDT_FIX_TOP(10), DW_WDT_FIX_TOP(11),
+	DW_WDT_FIX_TOP(12), DW_WDT_FIX_TOP(13), DW_WDT_FIX_TOP(14),
+	DW_WDT_FIX_TOP(15)
+};
+
 static bool nowayout = WATCHDOG_NOWAYOUT;
 module_param(nowayout, bool, 0);
 MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
 		 "(default=" __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
 
+struct dw_wdt_timeout {
+	u32 top_val;
+	unsigned int sec;
+	unsigned int msec;
+};
+
 struct dw_wdt {
 	void __iomem		*regs;
 	struct clk		*clk;
 	unsigned long		rate;
+	struct dw_wdt_timeout	timeouts[DW_WDT_NUM_TOPS];
 	struct watchdog_device	wdd;
 	struct reset_control	*rst;
 	/* Save/restore */
@@ -64,20 +85,66 @@ static inline int dw_wdt_is_enabled(struct dw_wdt *dw_wdt)
 		WDOG_CONTROL_REG_WDT_EN_MASK;
 }
 
-static inline int dw_wdt_top_in_seconds(struct dw_wdt *dw_wdt, unsigned top)
+static unsigned int dw_wdt_find_best_top(struct dw_wdt *dw_wdt,
+					 unsigned int timeout, u32 *top_val)
 {
+	int idx;
+
 	/*
-	 * There are 16 possible timeout values in 0..15 where the number of
-	 * cycles is 2 ^ (16 + i) and the watchdog counts down.
+	 * Find a TOP with timeout greater or equal to the requested number.
+	 * Note we'll select a TOP with maximum timeout if the requested
+	 * timeout couldn't be reached.
 	 */
-	return (1U << (16 + top)) / dw_wdt->rate;
+	for (idx = 0; idx < DW_WDT_NUM_TOPS; ++idx) {
+		if (dw_wdt->timeouts[idx].sec >= timeout)
+			break;
+	}
+
+	if (idx == DW_WDT_NUM_TOPS)
+		--idx;
+
+	*top_val = dw_wdt->timeouts[idx].top_val;
+
+	return dw_wdt->timeouts[idx].sec;
 }
 
-static int dw_wdt_get_top(struct dw_wdt *dw_wdt)
+static unsigned int dw_wdt_get_min_timeout(struct dw_wdt *dw_wdt)
 {
-	int top = readl(dw_wdt->regs + WDOG_TIMEOUT_RANGE_REG_OFFSET) & 0xF;
+	int idx;
+
+	/*
+	 * We'll find a timeout greater or equal to one second anyway because
+	 * the driver probe would have failed if there was none.
+	 */
+	for (idx = 0; idx < DW_WDT_NUM_TOPS; ++idx) {
+		if (dw_wdt->timeouts[idx].sec)
+			break;
+	}
 
-	return dw_wdt_top_in_seconds(dw_wdt, top);
+	return dw_wdt->timeouts[idx].sec;
+}
+
+static unsigned int dw_wdt_get_max_timeout_ms(struct dw_wdt *dw_wdt)
+{
+	struct dw_wdt_timeout *timeout = &dw_wdt->timeouts[DW_WDT_NUM_TOPS - 1];
+	u64 msec;
+
+	msec = (u64)timeout->sec * MSEC_PER_SEC + timeout->msec;
+
+	return msec < UINT_MAX ? msec : UINT_MAX;
+}
+
+static unsigned int dw_wdt_get_timeout(struct dw_wdt *dw_wdt)
+{
+	int top_val = readl(dw_wdt->regs + WDOG_TIMEOUT_RANGE_REG_OFFSET) & 0xF;
+	int idx;
+
+	for (idx = 0; idx < DW_WDT_NUM_TOPS; ++idx) {
+		if (dw_wdt->timeouts[idx].top_val == top_val)
+			break;
+	}
+
+	return dw_wdt->timeouts[idx].sec;
 }
 
 static int dw_wdt_ping(struct watchdog_device *wdd)
@@ -93,17 +160,10 @@ static int dw_wdt_ping(struct watchdog_device *wdd)
 static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int top_s)
 {
 	struct dw_wdt *dw_wdt = to_dw_wdt(wdd);
-	int i, top_val = DW_WDT_MAX_TOP;
+	unsigned int timeout;
+	u32 top_val;
 
-	/*
-	 * Iterate over the timeout values until we find the closest match. We
-	 * always look for >=.
-	 */
-	for (i = 0; i <= DW_WDT_MAX_TOP; ++i)
-		if (dw_wdt_top_in_seconds(dw_wdt, i) >= top_s) {
-			top_val = i;
-			break;
-		}
+	timeout = dw_wdt_find_best_top(dw_wdt, top_s, &top_val);
 
 	/*
 	 * Set the new value in the watchdog.  Some versions of dw_wdt
@@ -120,7 +180,7 @@ static int dw_wdt_set_timeout(struct watchdog_device *wdd, unsigned int top_s)
 	 * wdd->max_hw_heartbeat_ms
 	 */
 	if (top_s * 1000 <= wdd->max_hw_heartbeat_ms)
-		wdd->timeout = dw_wdt_top_in_seconds(dw_wdt, top_val);
+		wdd->timeout = timeout;
 	else
 		wdd->timeout = top_s;
 
@@ -238,6 +298,86 @@ static int dw_wdt_resume(struct device *dev)
 
 static SIMPLE_DEV_PM_OPS(dw_wdt_pm_ops, dw_wdt_suspend, dw_wdt_resume);
 
+/*
+ * In case if DW WDT IP core is synthesized with fixed TOP feature disabled the
+ * TOPs array can be arbitrary ordered with nearly any sixteen uint numbers
+ * depending on the system engineer imagination. The next method handles the
+ * passed TOPs array to pre-calculate the effective timeouts and to sort the
+ * TOP items out in the ascending order with respect to the timeouts.
+ */
+
+static void dw_wdt_handle_tops(struct dw_wdt *dw_wdt, const u32 *tops)
+{
+	struct dw_wdt_timeout tout, *dst;
+	int val, tidx;
+	u64 msec;
+
+	/*
+	 * We walk over the passed TOPs array and calculate corresponding
+	 * timeouts in seconds and milliseconds. The milliseconds granularity
+	 * is needed to distinguish the TOPs with very close timeouts and to
+	 * set the watchdog max heartbeat setting further.
+	 */
+	for (val = 0; val < DW_WDT_NUM_TOPS; ++val) {
+		tout.top_val = val;
+		tout.sec = tops[val] / dw_wdt->rate;
+		msec = (u64)tops[val] * MSEC_PER_SEC;
+		do_div(msec, dw_wdt->rate);
+		tout.msec = msec - ((u64)tout.sec * MSEC_PER_SEC);
+
+		/*
+		 * Find a suitable place for the current TOP in the timeouts
+		 * array so that the list is remained in the ascending order.
+		 */
+		for (tidx = 0; tidx < val; ++tidx) {
+			dst = &dw_wdt->timeouts[tidx];
+			if (tout.sec > dst->sec || (tout.sec == dst->sec &&
+			    tout.msec >= dst->msec))
+				continue;
+			else
+				swap(*dst, tout);
+		}
+
+		dw_wdt->timeouts[val] = tout;
+	}
+}
+
+static int dw_wdt_init_timeouts(struct dw_wdt *dw_wdt, struct device *dev)
+{
+	u32 data, of_tops[DW_WDT_NUM_TOPS];
+	const u32 *tops;
+	int ret;
+
+	/*
+	 * Retrieve custom or fixed counter values depending on the
+	 * WDT_USE_FIX_TOP flag found in the component specific parameters
+	 * #1 register.
+	 */
+	data = readl(dw_wdt->regs + WDOG_COMP_PARAMS_1_REG_OFFSET);
+	if (data & WDOG_COMP_PARAMS_1_USE_FIX_TOP) {
+		tops = dw_wdt_fix_tops;
+	} else {
+		ret = of_property_read_variable_u32_array(dev_of_node(dev),
+			"snps,watchdog-tops", of_tops, DW_WDT_NUM_TOPS,
+			DW_WDT_NUM_TOPS);
+		if (ret < 0) {
+			dev_warn(dev, "No valid TOPs array specified\n");
+			tops = dw_wdt_fix_tops;
+		} else {
+			tops = of_tops;
+		}
+	}
+
+	/* Convert the specified TOPs into an array of watchdog timeouts. */
+	dw_wdt_handle_tops(dw_wdt, tops);
+	if (!dw_wdt->timeouts[DW_WDT_NUM_TOPS - 1].sec) {
+		dev_err(dev, "No any valid TOP detected\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int dw_wdt_drv_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
@@ -275,12 +415,15 @@ static int dw_wdt_drv_probe(struct platform_device *pdev)
 
 	reset_control_deassert(dw_wdt->rst);
 
+	ret = dw_wdt_init_timeouts(dw_wdt, dev);
+	if (ret)
+		goto out_disable_clk;
+
 	wdd = &dw_wdt->wdd;
 	wdd->info = &dw_wdt_ident;
 	wdd->ops = &dw_wdt_ops;
-	wdd->min_timeout = 1;
-	wdd->max_hw_heartbeat_ms =
-		dw_wdt_top_in_seconds(dw_wdt, DW_WDT_MAX_TOP) * 1000;
+	wdd->min_timeout = dw_wdt_get_min_timeout(dw_wdt);
+	wdd->max_hw_heartbeat_ms = dw_wdt_get_max_timeout_ms(dw_wdt);
 	wdd->parent = dev;
 
 	watchdog_set_drvdata(wdd, dw_wdt);
@@ -293,7 +436,7 @@ static int dw_wdt_drv_probe(struct platform_device *pdev)
 	 * devicetree.
 	 */
 	if (dw_wdt_is_enabled(dw_wdt)) {
-		wdd->timeout = dw_wdt_get_top(dw_wdt);
+		wdd->timeout = dw_wdt_get_timeout(dw_wdt);
 		set_bit(WDOG_HW_RUNNING, &wdd->status);
 	} else {
 		wdd->timeout = DW_WDT_DEFAULT_SECONDS;