watchdog: Add support for K3 RTI watchdog

This is based on the Linux kernel driver for the RTI watchdog.

To actually reset the system on an AM65x, it requires firmware running
on the R5 that accepts the NMI and issues the actual system reset via
TISCI. Kind of an iTCO, except that this watchdog hardware has support
for no-way-out, and only for that.

On the J721E, reset works without extra firmware help when routing the
RTI interrupt via the ESM.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

drivers/watchdog/Kconfig

@@ -155,6 +155,13 @@ config WDT_ORION
 	  Select this to enable Orion watchdog timer, which can be found on some
 	  Marvell Armada chips.
 
+config WDT_K3_RTI
+	bool "Texas Instruments K3 RTI watchdog"
+	depends on WDT && ARCH_K3
+	help
+	  Say Y here if you want to include support for the K3 watchdog
+	  timer (RTI module) available in the K3 generation of processors.
+
 config WDT_SANDBOX
 	bool "Enable Watchdog Timer support for Sandbox"
 	depends on SANDBOX && WDT

drivers/watchdog/Makefile

@@ -28,6 +28,7 @@ obj-$(CONFIG_WDT_MT7621) += mt7621_wdt.o
 obj-$(CONFIG_WDT_MTK) += mtk_wdt.o
 obj-$(CONFIG_WDT_OMAP3) += omap_wdt.o
 obj-$(CONFIG_WDT_SBSA) += sbsa_gwdt.o
+obj-$(CONFIG_WDT_K3_RTI) += rti_wdt.o
 obj-$(CONFIG_WDT_SP805) += sp805_wdt.o
 obj-$(CONFIG_WDT_STM32MP) += stm32mp_wdt.o
 obj-$(CONFIG_WDT_TANGIER) += tangier_wdt.o

drivers/watchdog/rti_wdt.c

@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) Siemens AG, 2020
+ *
+ * Authors:
+ *   Jan Kiszka <jan.kiszka@siemens.com>
+ *
+ * Derived from linux/drivers/watchdog/rti_wdt.c
+ */
+
+#include <common.h>
+#include <clk.h>
+#include <dm.h>
+#include <power-domain.h>
+#include <wdt.h>
+#include <asm/io.h>
+
+/* Timer register set definition */
+#define RTIDWDCTRL		0x90
+#define RTIDWDPRLD		0x94
+#define RTIWDSTATUS		0x98
+#define RTIWDKEY		0x9c
+#define RTIDWDCNTR		0xa0
+#define RTIWWDRXCTRL		0xa4
+#define RTIWWDSIZECTRL		0xa8
+
+#define RTIWWDRX_NMI		0xa
+
+#define RTIWWDSIZE_50P		0x50
+
+#define WDENABLE_KEY		0xa98559da
+
+#define WDKEY_SEQ0		0xe51a
+#define WDKEY_SEQ1		0xa35c
+
+#define WDT_PRELOAD_SHIFT	13
+
+#define WDT_PRELOAD_MAX		0xfff
+
+struct rti_wdt_priv {
+	phys_addr_t regs;
+	unsigned int clk_khz;
+};
+
+static int rti_wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)
+{
+	struct rti_wdt_priv *priv = dev_get_priv(dev);
+	u32 timer_margin;
+	int ret;
+
+	if (readl(priv->regs + RTIDWDCTRL) == WDENABLE_KEY)
+		return -EBUSY;
+
+	timer_margin = timeout_ms * priv->clk_khz / 1000;
+	timer_margin >>= WDT_PRELOAD_SHIFT;
+	if (timer_margin > WDT_PRELOAD_MAX)
+		timer_margin = WDT_PRELOAD_MAX;
+
+	writel(timer_margin, priv->regs + RTIDWDPRLD);
+	writel(RTIWWDRX_NMI, priv->regs + RTIWWDRXCTRL);
+	writel(RTIWWDSIZE_50P, priv->regs + RTIWWDSIZECTRL);
+
+	readl(priv->regs + RTIWWDSIZECTRL);
+
+	writel(WDENABLE_KEY, priv->regs + RTIDWDCTRL);
+
+	return 0;
+}
+
+static int rti_wdt_reset(struct udevice *dev)
+{
+	struct rti_wdt_priv *priv = dev_get_priv(dev);
+	u32 prld;
+
+	/* Make sure we do not reset too early */
+	prld = readl(priv->regs + RTIDWDPRLD) << WDT_PRELOAD_SHIFT;
+	if (readl(priv->regs + RTIDWDCNTR) >= prld / 2)
+		return -EPERM;
+
+	writel(WDKEY_SEQ0, priv->regs + RTIWDKEY);
+	writel(WDKEY_SEQ1, priv->regs + RTIWDKEY);
+
+	return 0;
+}
+
+static int rti_wdt_probe(struct udevice *dev)
+{
+	struct rti_wdt_priv *priv = dev_get_priv(dev);
+	struct clk clk;
+	int ret;
+
+	priv->regs = devfdt_get_addr(dev);
+	if (!priv->regs)
+		return -EINVAL;
+
+	ret = clk_get_by_index(dev, 0, &clk);
+	if (ret)
+		return ret;
+
+	priv->clk_khz = clk_get_rate(&clk);
+
+	return 0;
+}
+
+static const struct wdt_ops rti_wdt_ops = {
+	.start = rti_wdt_start,
+	.reset = rti_wdt_reset,
+};
+
+static const struct udevice_id rti_wdt_ids[] = {
+	{ .compatible = "ti,j7-rti-wdt" },
+	{ }
+};
+
+U_BOOT_DRIVER(rti_wdt) = {
+	.name = "rti_wdt",
+	.id = UCLASS_WDT,
+	.of_match = rti_wdt_ids,
+	.ops = &rti_wdt_ops,
+	.probe = rti_wdt_probe,
+	.priv_auto_alloc_size = sizeof(struct rti_wdt_priv),
+	.flags = DM_FLAG_REMOVE_WITH_PD_ON,
+};