[v1,4/4] watchdog/pseries-wdt: initial support for PAPR H_WATCHDOG timers

diff --git a/Documentation/watchdog/watchdog-parameters.rst b/Documentation/watchdog/watchdog-parameters.rst
index 223c99361a30..4ffe725e796c 100644
--- a/Documentation/watchdog/watchdog-parameters.rst
+++ b/Documentation/watchdog/watchdog-parameters.rst
@@ -425,6 +425,18 @@  pnx833x_wdt:
 
 -------------------------------------------------
 
+pseries-wdt:
+    action:
+	Action taken when watchdog expires: 1 (power off), 2 (restart),
+	3 (dump and restart). (default=2)
+    timeout:
+	Initial watchdog timeout in seconds. (default=60)
+    nowayout:
+	Watchdog cannot be stopped once started.
+	(default=kernel config parameter)
+
+-------------------------------------------------
+
 rc32434_wdt:
     timeout:
 	Watchdog timeout value, in seconds (default=20)
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index c4e82a8d863f..06b412603f3e 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -1932,6 +1932,14 @@  config MEN_A21_WDT
 
 # PPC64 Architecture
 
+config PSERIES_WDT
+	tristate "POWER Architecture Platform Watchdog Timer"
+	depends on PPC_PSERIES
+	select WATCHDOG_CORE
+	help
+	  Driver for virtual watchdog timers provided by PAPR
+	  hypervisors (e.g. PowerVM, KVM).
+
 config WATCHDOG_RTAS
 	tristate "RTAS watchdog"
 	depends on PPC_RTAS
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index f7da867e8782..f35660409f17 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -184,6 +184,7 @@  obj-$(CONFIG_BOOKE_WDT) += booke_wdt.o
 obj-$(CONFIG_MEN_A21_WDT) += mena21_wdt.o
 
 # PPC64 Architecture
+obj-$(CONFIG_PSERIES_WDT) += pseries-wdt.o
 obj-$(CONFIG_WATCHDOG_RTAS) += wdrtas.o
 
 # S390 Architecture
diff --git a/drivers/watchdog/pseries-wdt.c b/drivers/watchdog/pseries-wdt.c
new file mode 100644
index 000000000000..f41bc4d3b7a2
--- /dev/null
+++ b/drivers/watchdog/pseries-wdt.c
@@ -0,0 +1,337 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2022 International Business Machines, Inc.
+ */
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <linux/limits.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/platform_device.h>
+#include <linux/watchdog.h>
+
+#define DRV_NAME "pseries-wdt"
+
+/*
+ * The PAPR's MSB->LSB bit ordering is 0->63.  These macros simplify
+ * defining bitfields as described in the PAPR without needing to
+ * transpose values to the more C-like 63->0 ordering.
+ */
+#define SETFIELD(_v, _b, _e)	\
+	(((unsigned long)(_v) << PPC_BITLSHIFT(_e)) & PPC_BITMASK((_b), (_e)))
+#define GETFIELD(_v, _b, _e)	\
+	(((unsigned long)(_v) & PPC_BITMASK((_b), (_e))) >> PPC_BITLSHIFT(_e))
+
+/*
+ * H_WATCHDOG Hypercall Input
+ *
+ * R4: "flags":
+ *
+ *     A 64-bit value structured as follows:
+ *
+ *         Bits 0-46: Reserved (must be zero).
+ */
+#define PSERIES_WDTF_RESERVED	PPC_BITMASK(0, 46)
+
+/*
+ *         Bit 47: "leaveOtherWatchdogsRunningOnTimeout"
+ *
+ *             0  Stop outstanding watchdogs on timeout.
+ *             1  Leave outstanding watchdogs running on timeout.
+ */
+#define PSERIES_WDTF_LEAVE_OTHER	PPC_BIT(47)
+
+/*
+ *         Bits 48-55: "operation"
+ *
+ *             0x01  Start Watchdog
+ *             0x02  Stop Watchdog
+ *             0x03  Query Watchdog Capabilities
+ *             0x04  Query Watchdog LPM Requirement
+ */
+#define PSERIES_WDTF_OP(op)		SETFIELD((op), 48, 55)
+#define PSERIES_WDTF_OP_START		PSERIES_WDTF_OP(0x1)
+#define PSERIES_WDTF_OP_STOP		PSERIES_WDTF_OP(0x2)
+#define PSERIES_WDTF_OP_QUERY		PSERIES_WDTF_OP(0x3)
+#define PSERIES_WDTF_OP_QUERY_LPM	PSERIES_WDTF_OP(0x4)
+
+/*
+ *         Bits 56-63: "timeoutAction"
+ *
+ *             0x01  Hard poweroff
+ *             0x02  Hard restart
+ *             0x03  Dump restart
+ */
+#define PSERIES_WDTF_ACTION(ac)			SETFIELD(ac, 56, 63)
+#define PSERIES_WDTF_ACTION_HARD_POWEROFF	PSERIES_WDTF_ACTION(0x1)
+#define PSERIES_WDTF_ACTION_HARD_RESTART	PSERIES_WDTF_ACTION(0x2)
+#define PSERIES_WDTF_ACTION_DUMP_RESTART	PSERIES_WDTF_ACTION(0x3)
+
+/*
+ * R5: "watchdogNumber":
+ *
+ *     The target watchdog.  Watchdog numbers are 1-based.  The
+ *     maximum supported watchdog number may be obtained via the
+ *     "Query Watchdog Capabilities" operation.
+ *
+ *     This input is ignored for the "Query Watchdog Capabilities"
+ *     operation.
+ *
+ * R6: "timeoutInMs":
+ *
+ *     The timeout in milliseconds.  The minimum supported timeout may
+ *     be obtained via the "Query Watchdog Capabilities" operation.
+ *
+ *     This input is ignored for the "Stop Watchdog", "Query Watchdog
+ *     Capabilities", and "Query Watchdog LPM Requirement" operations.
+ */
+
+/*
+ * H_WATCHDOG Hypercall Output
+ *
+ * R3: Return code
+ *
+ *     H_SUCCESS    The operation completed.
+ *
+ *     H_BUSY	    The hypervisor is too busy; retry the operation.
+ *
+ *     H_PARAMETER  The given "flags" are somehow invalid.  Either the
+ *                  "operation" or "timeoutAction" is invalid, or a
+ *                  reserved bit is set.
+ *
+ *     H_P2         The given "watchdogNumber" is zero or exceeds the
+ *                  supported maximum value.
+ *
+ *     H_P3         The given "timeoutInMs" is below the supported
+ *                  minimum value.
+ *
+ *     H_NOOP       The given "watchdogNumber" is already stopped.
+ *
+ *     H_HARDWARE   The operation failed for ineffable reasons.
+ *
+ *     H_FUNCTION   The H_WATCHDOG hypercall is not supported by this
+ *                  hypervisor.
+ *
+ * R4:
+ *
+ * - For the "Query Watchdog Capabilities" operation, a 64-bit
+ *   value structured as follows:
+ *
+ *       Bits  0-15: The minimum supported timeout in milliseconds.
+ *       Bits 16-31: The number of watchdogs supported.
+ *       Bits 32-63: Reserved.
+ */
+#define PSERIES_WDTQ_MIN_TIMEOUT(cap)	GETFIELD((cap), 0, 15)
+#define PSERIES_WDTQ_MAX_NUMBER(cap)	GETFIELD((cap), 16, 31)
+#define PSERIES_WDTQ_RESERVED		PPC_BITMASK(32, 63)
+
+/*
+ * - For the "Query Watchdog LPM Requirement" operation:
+ *
+ *       1  The given "watchdogNumber" must be stopped prior to
+ *          suspending.
+ *
+ *       2  The given "watchdogNumber" does not have to be stopped
+ *          prior to suspending.
+ */
+#define PSERIES_WDTQL_MUST_STOP		1
+#define PSERIES_WDTQL_NEED_NOT_STOP	2
+
+static unsigned long action = PSERIES_WDTF_ACTION_HARD_RESTART;
+
+static int action_get(char *buf, const struct kernel_param *kp)
+{
+	int val;
+
+	switch (action) {
+	case PSERIES_WDTF_ACTION_HARD_POWEROFF:
+		val = 1;
+		break;
+	case PSERIES_WDTF_ACTION_HARD_RESTART:
+		val = 2;
+		break;
+	case PSERIES_WDTF_ACTION_DUMP_RESTART:
+		val = 3;
+		break;
+	default:
+		return -EINVAL;
+	}
+	return sprintf(buf, "%d\n", val);
+}
+
+static int action_set(const char *val, const struct kernel_param *kp)
+{
+	int choice;
+
+	if (kstrtoint(val, 10, &choice))
+		return -EINVAL;
+	switch (choice) {
+	case 1:
+		action = PSERIES_WDTF_ACTION_HARD_POWEROFF;
+		return 0;
+	case 2:
+		action = PSERIES_WDTF_ACTION_HARD_RESTART;
+		return 0;
+	case 3:
+		action = PSERIES_WDTF_ACTION_DUMP_RESTART;
+		return 0;
+	}
+	return -EINVAL;
+}
+
+static const struct kernel_param_ops action_ops = {
+	.get = action_get,
+	.set = action_set,
+};
+module_param_cb(action, &action_ops, NULL, 0444);
+MODULE_PARM_DESC(action, "Action taken when watchdog expires (default=2)");
+
+static bool nowayout = WATCHDOG_NOWAYOUT;
+module_param(nowayout, bool, 0444);
+MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
+		 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
+
+#define WATCHDOG_TIMEOUT 60
+static unsigned int timeout = WATCHDOG_TIMEOUT;
+module_param(timeout, uint, 0444);
+MODULE_PARM_DESC(timeout, "Initial watchdog timeout in seconds (default="
+		 __MODULE_STRING(WATCHDOG_TIMEOUT) ")");
+
+struct pseries_wdt {
+	struct watchdog_device wd;
+	unsigned long num;		/* Watchdog numbers are 1-based */
+};
+
+static int pseries_wdt_start(struct watchdog_device *wdd)
+{
+	struct device *dev = wdd->parent;
+	struct pseries_wdt *pw = watchdog_get_drvdata(wdd);
+	unsigned long flags, msecs;
+	long rc;
+
+	flags = action | PSERIES_WDTF_OP_START;
+	msecs = wdd->timeout * 1000UL;
+	rc = plpar_hcall_norets(H_WATCHDOG, flags, pw->num, msecs);
+	if (rc != H_SUCCESS) {
+		dev_crit(dev, "H_WATCHDOG: %ld: failed to start timer %lu",
+			 rc, pw->num);
+		return -EIO;
+	}
+	return 0;
+}
+
+static int pseries_wdt_stop(struct watchdog_device *wdd)
+{
+	struct device *dev = wdd->parent;
+	struct pseries_wdt *pw = watchdog_get_drvdata(wdd);
+	long rc;
+
+	rc = plpar_hcall_norets(H_WATCHDOG, PSERIES_WDTF_OP_STOP, pw->num);
+	if (rc != H_SUCCESS && rc != H_NOOP) {
+		dev_crit(dev, "H_WATCHDOG: %ld: failed to stop timer %lu",
+			 rc, pw->num);
+		return -EIO;
+	}
+	return 0;
+}
+
+static struct watchdog_info pseries_wdt_info = {
+	.identity = DRV_NAME,
+	.options = WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE | WDIOF_SETTIMEOUT
+	    | WDIOF_PRETIMEOUT,
+};
+
+static const struct watchdog_ops pseries_wdt_ops = {
+	.owner = THIS_MODULE,
+	.start = pseries_wdt_start,
+	.stop = pseries_wdt_stop,
+};
+
+static int pseries_wdt_probe(struct platform_device *pdev)
+{
+	unsigned long ret[PLPAR_HCALL_BUFSIZE] = { 0 };
+	unsigned long cap, min_timeout_ms;
+	long rc;
+	struct pseries_wdt *pw;
+	int err;
+
+	rc = plpar_hcall(H_WATCHDOG, ret, PSERIES_WDTF_OP_QUERY);
+	if (rc != H_SUCCESS)
+		return rc == H_FUNCTION ? -ENODEV : -EIO;
+	cap = ret[0];
+
+	pw = devm_kzalloc(&pdev->dev, sizeof(*pw), GFP_KERNEL);
+	if (!pw)
+		return -ENOMEM;
+
+	/*
+	 * Assume watchdogNumber 1 for now.  If we ever support
+	 * multiple timers we will need to devise a way to choose a
+	 * distinct watchdogNumber for each platform device at device
+	 * registration time.
+	 */
+	pw->num = 1;
+
+	pw->wd.parent = &pdev->dev;
+	pw->wd.info = &pseries_wdt_info;
+	pw->wd.ops = &pseries_wdt_ops;
+	min_timeout_ms = PSERIES_WDTQ_MIN_TIMEOUT(cap);
+	pw->wd.min_timeout = roundup(min_timeout_ms, 1000) / 1000;
+	pw->wd.max_timeout = UINT_MAX;
+	watchdog_init_timeout(&pw->wd, timeout, NULL);
+	watchdog_set_nowayout(&pw->wd, nowayout);
+	watchdog_stop_on_reboot(&pw->wd);
+	watchdog_stop_on_unregister(&pw->wd);
+	watchdog_set_drvdata(&pw->wd, pw);
+
+	err = devm_watchdog_register_device(&pdev->dev, &pw->wd);
+	if (err)
+		return err;
+
+	platform_set_drvdata(pdev, &pw->wd);
+
+	return 0;
+}
+
+static int pseries_wdt_suspend(struct platform_device *pdev, pm_message_t state)
+{
+	struct watchdog_device *wd = platform_get_drvdata(pdev);
+
+	if (watchdog_active(wd))
+		return pseries_wdt_stop(wd);
+	return 0;
+}
+
+static int pseries_wdt_resume(struct platform_device *pdev)
+{
+	struct watchdog_device *wd = platform_get_drvdata(pdev);
+
+	if (watchdog_active(wd))
+		return pseries_wdt_start(wd);
+	return 0;
+}
+
+static const struct platform_device_id pseries_wdt_id[] = {
+	{ .name = "pseries-wdt" },
+	{}
+};
+MODULE_DEVICE_TABLE(platform, pseries_wdt_id);
+
+static struct platform_driver pseries_wdt_driver = {
+	.driver = {
+		.name = DRV_NAME,
+		.owner = THIS_MODULE,
+	},
+	.id_table = pseries_wdt_id,
+	.probe = pseries_wdt_probe,
+	.resume = pseries_wdt_resume,
+	.suspend = pseries_wdt_suspend,
+};
+module_platform_driver(pseries_wdt_driver);
+
+MODULE_AUTHOR("Alexey Kardashevskiy <aik@ozlabs.ru>");
+MODULE_AUTHOR("Scott Cheloha <cheloha@linux.ibm.com>");
+MODULE_DESCRIPTION("POWER Architecture Platform Watchdog Driver");
+MODULE_LICENSE("GPL");