[PATCH v3 2/2] watchdog: pic32-wdt: Add PIC32 watchdog driver

[Joshua Henderson]

Add support for the watchdog peripheral found on PIC32 class
devices.

Signed-off-by: Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx>
Signed-off-by: Purna Chandra Mandal <purna.mandal@xxxxxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
---
Note: Please merge this patch series through the MIPS tree.

Changes since v2:
	- Remove pr_fmt and replace pr_debug with dev_dbg
	- Check whether rate is zero later when looking for div/zero
	- Be consistent and return u32 on pic32_wdt_get_timeout_secs()
	- Use -ENODEV instead of -EOPNOTSUPP in probe failure
Changes since v1:
	- Shorten commit description
	- Don't default to y in Kconfig
	- Alphabetical ordering of includes
	- Use BIT() where applicable
	- Use consistent function name prefixes
	- Inline some single use functions
	- Use a return of bool when appropriate
	- Replace cpu_relax() with nop and explain why this is needed
	- Better error handling, especially to prevent divide by zero
	- Remove unecessary pr_info().
	- Remove redudant driver spinlock which is already covered by
	  watchdog core
	- Drop .get_timeleft implementation
	- Fix typo in compatibility flag and driver name
	- Remove wdt->timeout variable and calculation
	- Fix race condition in watchdog driver registration
---
 drivers/watchdog/Kconfig     |   13 +++
 drivers/watchdog/Makefile    |    1 +
 drivers/watchdog/pic32-wdt.c |  263 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 277 insertions(+)
 create mode 100644 drivers/watchdog/pic32-wdt.c

diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 0f6d851..543fa81 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -1414,6 +1414,19 @@ config MT7621_WDT
 	help
 	  Hardware driver for the Mediatek/Ralink MT7621/8 SoC Watchdog Timer.
 
+config PIC32_WDT
+	tristate "Microchip PIC32 hardware watchdog"
+	select WATCHDOG_CORE
+	depends on MACH_PIC32
+	help
+	  Watchdog driver for the built in watchdog hardware in a PIC32.
+
+	  Configuration bits must be set appropriately for the watchdog to be
+	  controlled by this driver.
+
+	  To compile this driver as a loadable module, choose M here.
+	  The module will be called pic32-wdt.
+
 # PARISC Architecture
 
 # POWERPC Architecture
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index f566753..244ed80 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -153,6 +153,7 @@ obj-$(CONFIG_LANTIQ_WDT) += lantiq_wdt.o
 obj-$(CONFIG_RALINK_WDT) += rt2880_wdt.o
 obj-$(CONFIG_IMGPDC_WDT) += imgpdc_wdt.o
 obj-$(CONFIG_MT7621_WDT) += mt7621_wdt.o
+obj-$(CONFIG_PIC32_WDT) += pic32-wdt.o
 
 # PARISC Architecture
 
diff --git a/drivers/watchdog/pic32-wdt.c b/drivers/watchdog/pic32-wdt.c
new file mode 100644
index 0000000..6047aa8
--- /dev/null
+++ b/drivers/watchdog/pic32-wdt.c
@@ -0,0 +1,263 @@
+/*
+ * PIC32 watchdog driver
+ *
+ * Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx>
+ * Copyright (c) 2016, Microchip Technology Inc.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/pm.h>
+#include <linux/watchdog.h>
+
+#include <asm/mach-pic32/pic32.h>
+
+/* Watchdog Timer Registers */
+#define WDTCON_REG		0x00
+
+/* Watchdog Timer Control Register fields */
+#define WDTCON_WIN_EN		BIT(0)
+#define WDTCON_RMCS_MASK	0x0003
+#define WDTCON_RMCS_SHIFT	0x0006
+#define WDTCON_RMPS_MASK	0x001F
+#define WDTCON_RMPS_SHIFT	0x0008
+#define WDTCON_ON		BIT(15)
+#define WDTCON_CLR_KEY		0x5743
+
+/* Reset Control Register fields for watchdog */
+#define RESETCON_TIMEOUT_IDLE	BIT(2)
+#define RESETCON_TIMEOUT_SLEEP	BIT(3)
+#define RESETCON_WDT_TIMEOUT	BIT(4)
+
+struct pic32_wdt {
+	void __iomem	*regs;
+	void __iomem	*rst_base;
+	struct clk	*clk;
+};
+
+static inline bool pic32_wdt_is_win_enabled(struct pic32_wdt *wdt)
+{
+	return !!(readl(wdt->regs + WDTCON_REG) & WDTCON_WIN_EN);
+}
+
+static inline u32 pic32_wdt_get_post_scaler(struct pic32_wdt *wdt)
+{
+	u32 v = readl(wdt->regs + WDTCON_REG);
+
+	return (v >> WDTCON_RMPS_SHIFT) & WDTCON_RMPS_MASK;
+}
+
+static inline u32 pic32_wdt_get_clk_id(struct pic32_wdt *wdt)
+{
+	u32 v = readl(wdt->regs + WDTCON_REG);
+
+	return (v >> WDTCON_RMCS_SHIFT) & WDTCON_RMCS_MASK;
+}
+
+static int pic32_wdt_bootstatus(struct pic32_wdt *wdt)
+{
+	u32 v = readl(wdt->rst_base);
+
+	writel(RESETCON_WDT_TIMEOUT, PIC32_CLR(wdt->rst_base));
+
+	return v & RESETCON_WDT_TIMEOUT;
+}
+
+static u32 pic32_wdt_get_timeout_secs(struct pic32_wdt *wdt, struct device *dev)
+{
+	unsigned long rate;
+	u32 period, ps, terminal;
+
+	rate = clk_get_rate(wdt->clk);
+
+	dev_dbg(dev, "wdt: clk_id %d, clk_rate %lu (prescale)\n",
+		pic32_wdt_get_clk_id(wdt), rate);
+
+	/* default, prescaler of 32 (i.e. div-by-32) is implicit. */
+	rate >>= 5;
+	if (!rate)
+		return 0;
+
+	/* calculate terminal count from postscaler. */
+	ps = pic32_wdt_get_post_scaler(wdt);
+	terminal = BIT(ps);
+
+	/* find time taken (in secs) to reach terminal count */
+	period = terminal / rate;
+	dev_dbg(dev,
+		"wdt: clk_rate %lu (postscale) / terminal %d, timeout %dsec\n",
+		rate, terminal, period);
+
+	return period;
+}
+
+static void pic32_wdt_keepalive(struct pic32_wdt *wdt)
+{
+	/* write key through single half-word */
+	writew(WDTCON_CLR_KEY, wdt->regs + WDTCON_REG + 2);
+}
+
+static int pic32_wdt_start(struct watchdog_device *wdd)
+{
+	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	writel(WDTCON_ON, PIC32_SET(wdt->regs + WDTCON_REG));
+	pic32_wdt_keepalive(wdt);
+
+	return 0;
+}
+
+static int pic32_wdt_stop(struct watchdog_device *wdd)
+{
+	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	writel(WDTCON_ON, PIC32_CLR(wdt->regs + WDTCON_REG));
+
+	/*
+	 * Cannot touch registers in the CPU cycle following clearing the
+	 * ON bit.
+	 */
+	nop();
+
+	return 0;
+}
+
+static int pic32_wdt_ping(struct watchdog_device *wdd)
+{
+	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	pic32_wdt_keepalive(wdt);
+
+	return 0;
+}
+
+static const struct watchdog_ops pic32_wdt_fops = {
+	.owner		= THIS_MODULE,
+	.start		= pic32_wdt_start,
+	.stop		= pic32_wdt_stop,
+	.ping		= pic32_wdt_ping,
+};
+
+static const struct watchdog_info pic32_wdt_ident = {
+	.options = WDIOF_KEEPALIVEPING |
+			WDIOF_MAGICCLOSE | WDIOF_CARDRESET,
+	.identity = "PIC32 Watchdog",
+};
+
+static struct watchdog_device pic32_wdd = {
+	.info		= &pic32_wdt_ident,
+	.ops		= &pic32_wdt_fops,
+};
+
+static const struct of_device_id pic32_wdt_dt_ids[] = {
+	{ .compatible = "microchip,pic32mzda-wdt", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, pic32_wdt_dt_ids);
+
+static int pic32_wdt_drv_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct watchdog_device *wdd = &pic32_wdd;
+	struct pic32_wdt *wdt;
+	struct resource *mem;
+
+	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
+	if (IS_ERR(wdt))
+		return PTR_ERR(wdt);
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	wdt->regs = devm_ioremap_resource(&pdev->dev, mem);
+	if (IS_ERR(wdt->regs))
+		return PTR_ERR(wdt->regs);
+
+	wdt->rst_base = devm_ioremap(&pdev->dev, PIC32_BASE_RESET, 0x10);
+	if (IS_ERR(wdt->rst_base))
+		return PTR_ERR(wdt->rst_base);
+
+	wdt->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(wdt->clk)) {
+		dev_err(&pdev->dev, "clk not found\n");
+		return PTR_ERR(wdt->clk);
+	}
+
+	ret = clk_prepare_enable(wdt->clk);
+	if (ret) {
+		dev_err(&pdev->dev, "clk enable failed\n");
+		return ret;
+	}
+
+	if (pic32_wdt_is_win_enabled(wdt)) {
+		dev_err(&pdev->dev, "windowed-clear mode is not supported.\n");
+		ret = -ENODEV;
+		goto out_disable_clk;
+	}
+
+	wdd->timeout = pic32_wdt_get_timeout_secs(wdt, &pdev->dev);
+	if (!wdd->timeout) {
+		dev_err(&pdev->dev,
+			"failed to read watchdog register timeout\n");
+		ret = -EINVAL;
+		goto out_disable_clk;
+	}
+
+	dev_info(&pdev->dev, "timeout %d\n", wdd->timeout);
+
+	wdd->bootstatus = pic32_wdt_bootstatus(wdt) ? WDIOF_CARDRESET : 0;
+
+	watchdog_set_nowayout(wdd, WATCHDOG_NOWAYOUT);
+	watchdog_set_drvdata(wdd, wdt);
+
+	ret = watchdog_register_device(wdd);
+	if (ret) {
+		dev_err(&pdev->dev, "watchdog register failed, err %d\n", ret);
+		goto out_disable_clk;
+	}
+
+	platform_set_drvdata(pdev, wdd);
+
+	return 0;
+
+out_disable_clk:
+	clk_disable_unprepare(wdt->clk);
+
+	return ret;
+}
+
+static int pic32_wdt_drv_remove(struct platform_device *pdev)
+{
+	struct watchdog_device *wdd = platform_get_drvdata(pdev);
+	struct pic32_wdt *wdt = watchdog_get_drvdata(wdd);
+
+	watchdog_unregister_device(wdd);
+	clk_disable_unprepare(wdt->clk);
+
+	return 0;
+}
+
+static struct platform_driver pic32_wdt_driver = {
+	.probe		= pic32_wdt_drv_probe,
+	.remove		= pic32_wdt_drv_remove,
+	.driver		= {
+		.name		= "pic32-wdt",
+		.owner		= THIS_MODULE,
+		.of_match_table = of_match_ptr(pic32_wdt_dt_ids),
+	}
+};
+
+module_platform_driver(pic32_wdt_driver);
+
+MODULE_AUTHOR("Joshua Henderson <joshua.henderson@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Microchip PIC32 Watchdog Timer");
+MODULE_LICENSE("GPL");
-- 
1.7.9.5