watchdog: ts4800: add driver for TS-4800 watchdog

This watchdog is instantiated in a FPGA that is memory mapped. It is
made of only one register, called the feed register. Writing to this
register will re-arm the watchdog for a given time (and enable it if it
was disable). It can be disabled by writing a special value into it.

It is part of a syscon block, and the watchdog register offset in this
block varies from board to board. This offset is passed in the syscon
property after the phandle to the syscon node.

Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/ts4800-wdt.txt

@@ -0,0 +1,25 @@
+Technologic Systems Watchdog
+
+Required properties:
+- compatible: must be "technologic,ts4800-wdt"
+- syscon: phandle / integer array that points to the syscon node which
+          describes the FPGA's syscon registers.
+          - phandle to FPGA's syscon
+          - offset to the watchdog register
+
+Optional property:
+- timeout-sec: contains the watchdog timeout in seconds.
+
+Example:
+
+syscon: syscon@b0010000 {
+	compatible = "syscon", "simple-mfd";
+	reg = <0xb0010000 0x3d>;
+	reg-io-width = <2>;
+
+	wdt@e {
+		compatible = "technologic,ts4800-wdt";
+		syscon = <&syscon 0xe>;
+		timeout-sec = <10>;
+	};
+}

drivers/watchdog/Kconfig

@@ -433,6 +433,16 @@ config NUC900_WATCHDOG
 	  To compile this driver as a module, choose M here: the
 	  module will be called nuc900_wdt.
 
+config TS4800_WATCHDOG
+	tristate "TS-4800 Watchdog"
+	depends on HAS_IOMEM && OF
+	select WATCHDOG_CORE
+	select MFD_SYSCON
+	help
+	  Technologic Systems TS-4800 has watchdog timer implemented in
+	  an external FPGA. Say Y here if you want to support for the
+	  watchdog timer on TS-4800 board.
+
 config TS72XX_WATCHDOG
 	tristate "TS-72XX SBC Watchdog"
 	depends on MACH_TS72XX

drivers/watchdog/Makefile

@@ -53,6 +53,7 @@ obj-$(CONFIG_RN5T618_WATCHDOG) += rn5t618_wdt.o
 obj-$(CONFIG_COH901327_WATCHDOG) += coh901327_wdt.o
 obj-$(CONFIG_STMP3XXX_RTC_WATCHDOG) += stmp3xxx_rtc_wdt.o
 obj-$(CONFIG_NUC900_WATCHDOG) += nuc900_wdt.o
+obj-$(CONFIG_TS4800_WATCHDOG) += ts4800_wdt.o
 obj-$(CONFIG_TS72XX_WATCHDOG) += ts72xx_wdt.o
 obj-$(CONFIG_IMX2_WDT) += imx2_wdt.o
 obj-$(CONFIG_UX500_WATCHDOG) += ux500_wdt.o

drivers/watchdog/ts4800_wdt.c

@@ -0,0 +1,215 @@
+/*
+ * Watchdog driver for TS-4800 based boards
+ *
+ * Copyright (c) 2015 - Savoir-faire Linux
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include <linux/kernel.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/watchdog.h>
+
+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) ")");
+
+/* possible feed values */
+#define TS4800_WDT_FEED_2S       0x1
+#define TS4800_WDT_FEED_10S      0x2
+#define TS4800_WDT_DISABLE       0x3
+
+struct ts4800_wdt {
+	struct watchdog_device  wdd;
+	struct regmap           *regmap;
+	u32                     feed_offset;
+	u32                     feed_val;
+};
+
+/*
+ * TS-4800 supports the following timeout values:
+ *
+ *   value desc
+ *   ---------------------
+ *     0    feed for 338ms
+ *     1    feed for 2.706s
+ *     2    feed for 10.824s
+ *     3    disable watchdog
+ *
+ * Keep the regmap/timeout map ordered by timeout
+ */
+static const struct {
+	const int timeout;
+	const int regval;
+} ts4800_wdt_map[] = {
+	{ 2,  TS4800_WDT_FEED_2S },
+	{ 10, TS4800_WDT_FEED_10S },
+};
+
+#define MAX_TIMEOUT_INDEX       (ARRAY_SIZE(ts4800_wdt_map) - 1)
+
+static void ts4800_write_feed(struct ts4800_wdt *wdt, u32 val)
+{
+	regmap_write(wdt->regmap, wdt->feed_offset, val);
+}
+
+static int ts4800_wdt_start(struct watchdog_device *wdd)
+{
+	struct ts4800_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	ts4800_write_feed(wdt, wdt->feed_val);
+	return 0;
+}
+
+static int ts4800_wdt_stop(struct watchdog_device *wdd)
+{
+	struct ts4800_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	ts4800_write_feed(wdt, TS4800_WDT_DISABLE);
+	return 0;
+}
+
+static int ts4800_wdt_set_timeout(struct watchdog_device *wdd,
+				  unsigned int timeout)
+{
+	struct ts4800_wdt *wdt = watchdog_get_drvdata(wdd);
+	int i;
+
+	for (i = 0; i < MAX_TIMEOUT_INDEX; i++) {
+		if (ts4800_wdt_map[i].timeout >= timeout)
+			break;
+	}
+
+	wdd->timeout = ts4800_wdt_map[i].timeout;
+	wdt->feed_val = ts4800_wdt_map[i].regval;
+
+	return 0;
+}
+
+static const struct watchdog_ops ts4800_wdt_ops = {
+	.owner = THIS_MODULE,
+	.start = ts4800_wdt_start,
+	.stop = ts4800_wdt_stop,
+	.set_timeout = ts4800_wdt_set_timeout,
+};
+
+static const struct watchdog_info ts4800_wdt_info = {
+	.options = WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE | WDIOF_KEEPALIVEPING,
+	.identity = "TS-4800 Watchdog",
+};
+
+static int ts4800_wdt_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct device_node *syscon_np;
+	struct watchdog_device *wdd;
+	struct ts4800_wdt *wdt;
+	u32 reg;
+	int ret;
+
+	syscon_np = of_parse_phandle(np, "syscon", 0);
+	if (!syscon_np) {
+		dev_err(&pdev->dev, "no syscon property\n");
+		return -ENODEV;
+	}
+
+	ret = of_property_read_u32_index(np, "syscon", 1, &reg);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "no offset in syscon\n");
+		return ret;
+	}
+
+	/* allocate memory for watchdog struct */
+	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
+	if (!wdt)
+		return -ENOMEM;
+
+	/* set regmap and offset to know where to write */
+	wdt->feed_offset = reg;
+	wdt->regmap = syscon_node_to_regmap(syscon_np);
+	if (IS_ERR(wdt->regmap)) {
+		dev_err(&pdev->dev, "cannot get parent's regmap\n");
+		return PTR_ERR(wdt->regmap);
+	}
+
+	/* Initialize struct watchdog_device */
+	wdd = &wdt->wdd;
+	wdd->parent = &pdev->dev;
+	wdd->info = &ts4800_wdt_info;
+	wdd->ops = &ts4800_wdt_ops;
+	wdd->min_timeout = ts4800_wdt_map[0].timeout;
+	wdd->max_timeout = ts4800_wdt_map[MAX_TIMEOUT_INDEX].timeout;
+
+	watchdog_set_drvdata(wdd, wdt);
+	watchdog_set_nowayout(wdd, nowayout);
+	watchdog_init_timeout(wdd, 0, &pdev->dev);
+
+	/*
+	 * As this watchdog supports only a few values, ts4800_wdt_set_timeout
+	 * must be called to initialize timeout and feed_val with valid values.
+	 * Default to maximum timeout if none, or an invalid one, is provided in
+	 * device tree.
+	 */
+	if (!wdd->timeout)
+		wdd->timeout = wdd->max_timeout;
+	ts4800_wdt_set_timeout(wdd, wdd->timeout);
+
+	/*
+	 * The feed register is write-only, so it is not possible to determine
+	 * watchdog's state. Disable it to be in a known state.
+	 */
+	ts4800_wdt_stop(wdd);
+
+	ret = watchdog_register_device(wdd);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"failed to register watchdog device\n");
+		return ret;
+	}
+
+	platform_set_drvdata(pdev, wdt);
+
+	dev_info(&pdev->dev,
+		 "initialized (timeout = %d sec, nowayout = %d)\n",
+		 wdd->timeout, nowayout);
+
+	return 0;
+}
+
+static int ts4800_wdt_remove(struct platform_device *pdev)
+{
+	struct ts4800_wdt *wdt = platform_get_drvdata(pdev);
+
+	watchdog_unregister_device(&wdt->wdd);
+
+	return 0;
+}
+
+static const struct of_device_id ts4800_wdt_of_match[] = {
+	{ .compatible = "technologic,ts4800-wdt", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ts4800_wdt_of_match);
+
+static struct platform_driver ts4800_wdt_driver = {
+	.probe		= ts4800_wdt_probe,
+	.remove		= ts4800_wdt_remove,
+	.driver		= {
+		.name	= "ts4800_wdt",
+		.of_match_table = ts4800_wdt_of_match,
+	},
+};
+
+module_platform_driver(ts4800_wdt_driver);
+
+MODULE_AUTHOR("Damien Riegel <damien.riegel@savoirfairelinux.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:ts4800_wdt");