[PATCH v3 6/6] watchdog: ts4600: add driver for TS-4600 watchdog

[Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>]

This watchdog is instantiated in a FPGA and can only be access using a
GPIOs bit-banged bus, called the NBUS by Technologic Systems.
The watchdog 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.

Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
---
Changes v2 -> v3:
  - rebase on master
  - remove the timeout table to simplify the logic (suggested by
  Guenter Roeck)
  - fix the set_timeout function (suggested by Guenter Roeck)
  - hardcode the max_hw_heartbeat_ms value based on the ts4600 max
  timeout value supported (suggested by Guenter Roeck)
  - remove the max_timeout usage and set a default timeout value
(suggested by Guenter Roeck)
  - use the devm_watchdog_register_device function instead of
  watchdog_register_device (suggested by Guenter Roeck)

Changes v1 -> v2:
  - rebase on master
  - retrieve the ts_nbus instantiated by the parent node (suggested by
  Linus Walleij)
  - rename the wdt by watchdog in the device tree and in the
  documentation (suggested by Rob Herring)
  - add a dependency to the TS_NBUS driver in the Kconfig (suggested by
  Guenter Roeck)
  - simplify the set_timeout function (suggested by Guenter Roeck)
  - use the max_hw_heartbeat_ms callback instead of the max_timeout
  callback (suggested by Guenter Roeck)
---
 .../devicetree/bindings/watchdog/ts4600-wdt.txt    |  16 ++
 arch/arm/boot/dts/imx28-ts4600-common.dtsi         |   5 +
 drivers/watchdog/Kconfig                           |  11 ++
 drivers/watchdog/Makefile                          |   1 +
 drivers/watchdog/ts4600_wdt.c                      | 185 +++++++++++++++++++++
 5 files changed, 218 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/watchdog/ts4600-wdt.txt
 create mode 100644 drivers/watchdog/ts4600_wdt.c

diff --git a/Documentation/devicetree/bindings/watchdog/ts4600-wdt.txt b/Documentation/devicetree/bindings/watchdog/ts4600-wdt.txt
new file mode 100644
index 000000000000..7de00ceae341
--- /dev/null
+++ b/Documentation/devicetree/bindings/watchdog/ts4600-wdt.txt
@@ -0,0 +1,16 @@
+TS-4600 Technologic Systems Watchdog
+
+Required properties:
+- compatible: must be "technologic,ts4600-wdt"
+- reg: offset to the FPGA's watchdog register
+
+Optional property:
+- timeout-sec: contains the watchdog timeout in seconds.
+
+Example:
+
+watchdog {
+	compatible = "technologic,ts4600-wdt";
+	reg = <0x2a>;
+	timeout-sec = <10>;
+};
diff --git a/arch/arm/boot/dts/imx28-ts4600-common.dtsi b/arch/arm/boot/dts/imx28-ts4600-common.dtsi
index c6282d5479de..092c2eed0fe7 100644
--- a/arch/arm/boot/dts/imx28-ts4600-common.dtsi
+++ b/arch/arm/boot/dts/imx28-ts4600-common.dtsi
@@ -116,6 +116,11 @@
 		ts-strobe-gpios = <&gpio0 25 GPIO_ACTIVE_HIGH>;
 		ts-ale-gpios    = <&gpio0 26 GPIO_ACTIVE_HIGH>;
 		ts-rdy-gpios    = <&gpio0 21 GPIO_ACTIVE_HIGH>;
+
+		watchdog@2a {
+			compatible = "technologic,ts4600-wdt";
+			reg = <0x2a>;
+		};
 	};
 
 };
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 52a70ee6014f..408ad7c92cb3 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -520,6 +520,17 @@ config NUC900_WATCHDOG
 	  To compile this driver as a module, choose M here: the
 	  module will be called nuc900_wdt.
 
+config TS4600_WATCHDOG
+	tristate "TS-4600 Watchdog"
+	depends on TS_NBUS
+	depends on HAS_IOMEM && OF
+	depends on SOC_IMX28 || COMPILE_TEST
+	select WATCHDOG_CORE
+	help
+	  Technologic Systems TS-4600 has watchdog timer implemented in
+	  an external FPGA. Say Y here if you want to support for the
+	  watchdog timer on TS-4600 board.
+
 config TS4800_WATCHDOG
 	tristate "TS-4800 Watchdog"
 	depends on HAS_IOMEM && OF
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index a2126e2a99ae..19553f27061a 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -62,6 +62,7 @@ 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-$(CONFIG_TS4600_WATCHDOG) += ts4600_wdt.o
 obj-$(CONFIG_TS4800_WATCHDOG) += ts4800_wdt.o
 obj-$(CONFIG_TS72XX_WATCHDOG) += ts72xx_wdt.o
 obj-$(CONFIG_IMX2_WDT) += imx2_wdt.o
diff --git a/drivers/watchdog/ts4600_wdt.c b/drivers/watchdog/ts4600_wdt.c
new file mode 100644
index 000000000000..ed530dd2f800
--- /dev/null
+++ b/drivers/watchdog/ts4600_wdt.c
@@ -0,0 +1,185 @@
+/*
+ * Watchdog driver for TS-4600 based boards
+ *
+ * Copyright (c) 2016 - Savoir-faire Linux
+ * Author: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
+ *
+ * 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.
+ *
+ * The watchdog on the TS-4600 based boards is in an FPGA and can only be
+ * accessed using a GPIO bit-banged bus called the NBUS by Technologic Systems.
+ * The logic for the watchdog is the same then for the TS-4800 SoM, only the way
+ * to access it change, therefore this driver is heavely based on the ts4800_wdt
+ * driver from Damien Riegel <damien.riegel@savoirfairelinux.com>.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/ts-nbus.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) ")");
+
+/*
+ * TS-4600 supports the following timeout values:
+ *
+ *   value desc
+ *   ---------------------
+ *     0    feed for 338ms
+ *     1    feed for 2.706s
+ *     2    feed for 10.824s
+ *     3    disable watchdog
+ */
+#define TS4600_WDT_FEED_2S       0x1
+#define TS4600_WDT_FEED_10S      0x2
+#define TS4600_WDT_DISABLE       0x3
+
+struct ts4600_wdt {
+	struct watchdog_device  wdd;
+	struct ts_nbus		*ts_nbus;
+	u32                     feed_offset;
+	u32                     feed_val;
+};
+
+static void ts4600_write_feed(struct ts4600_wdt *wdt, u32 val)
+{
+	ts_nbus_write(wdt->ts_nbus, wdt->feed_offset, val);
+}
+
+static int ts4600_wdt_start(struct watchdog_device *wdd)
+{
+	struct ts4600_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	ts4600_write_feed(wdt, wdt->feed_val);
+
+	return 0;
+}
+
+static int ts4600_wdt_stop(struct watchdog_device *wdd)
+{
+	struct ts4600_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	ts4600_write_feed(wdt, TS4600_WDT_DISABLE);
+	return 0;
+}
+
+static int ts4600_wdt_set_timeout(struct watchdog_device *wdd,
+				  unsigned int timeout)
+{
+	struct ts4600_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	if (timeout <= 2) {
+		wdd->timeout = 2;
+		wdt->feed_val = TS4600_WDT_FEED_2S;
+	} else {
+		wdd->timeout = timeout < 10 ? 10 : timeout;
+		wdt->feed_val = TS4600_WDT_FEED_10S;
+	}
+
+	return 0;
+}
+
+static const struct watchdog_ops ts4600_wdt_ops = {
+	.owner = THIS_MODULE,
+	.start = ts4600_wdt_start,
+	.stop = ts4600_wdt_stop,
+	.set_timeout = ts4600_wdt_set_timeout,
+};
+
+static const struct watchdog_info ts4600_wdt_info = {
+	.options = WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE | WDIOF_KEEPALIVEPING,
+	.identity = "TS-4600 Watchdog",
+};
+
+static int ts4600_wdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct ts_nbus *ts_nbus;
+	struct watchdog_device *wdd;
+	struct ts4600_wdt *wdt;
+	u32 reg;
+	int ret;
+
+	ret = of_property_read_u32(np, "reg", &reg);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "missing reg property\n");
+		return ret;
+	}
+
+	/* allocate memory for watchdog struct */
+	wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
+	if (!wdt)
+		return -ENOMEM;
+
+	/* set offset to know where to write */
+	wdt->feed_offset = reg;
+
+	/* keep a pointer to the ts_nbus instanciated by the parent node */
+	ts_nbus = dev_get_drvdata(dev->parent);
+	if (!ts_nbus) {
+		dev_err(dev, "missing ts-nbus compatible parent node\n");
+		return PTR_ERR(ts_nbus);
+	}
+	wdt->ts_nbus = ts_nbus;
+
+	/* Initialize struct watchdog_device */
+	wdd = &wdt->wdd;
+	wdd->parent = dev;
+	wdd->info = &ts4600_wdt_info;
+	wdd->ops = &ts4600_wdt_ops;
+	wdd->min_timeout = 2;
+	wdd->max_hw_heartbeat_ms = 10824;
+	wdd->timeout = 30;
+
+	watchdog_set_drvdata(wdd, wdt);
+	watchdog_set_nowayout(wdd, nowayout);
+	watchdog_init_timeout(wdd, 0, dev);
+
+	ts4600_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.
+	 */
+	ts4600_wdt_stop(wdd);
+
+	ret = devm_watchdog_register_device(&pdev->dev, &wdt->wdd);
+	if (ret) {
+		dev_err(dev, "failed to register watchdog device\n");
+		return ret;
+	}
+
+	dev_info(dev, "initialized (timeout = %d sec, nowayout = %d)\n",
+		 wdd->timeout, nowayout);
+
+	return 0;
+}
+
+static const struct of_device_id ts4600_wdt_of_match[] = {
+	{ .compatible = "technologic,ts4600-wdt", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ts4600_wdt_of_match);
+
+static struct platform_driver ts4600_wdt_driver = {
+	.probe		= ts4600_wdt_probe,
+	.driver		= {
+		.name	= "ts4600_wdt",
+		.of_match_table = ts4600_wdt_of_match,
+	},
+};
+
+module_platform_driver(ts4600_wdt_driver);
+
+MODULE_AUTHOR("Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:ts4600_wdt");
-- 
2.12.0