watchdog: qcom: introduce qcom-wdt driver

Some Qualcomm device vendors decide to turn the watchdog on in the
bootloader, resulting in the device being reset if it isn't petted every
~30 seconds. Introduce a driver to keep the watchdog happy and prevent this
annoying behaviour.

Signed-off-by: Paul Sajna <hello@paulsajna.com>
Co-authored-by: Paul Sajna <hello@paulsajna.com>
Tested-by: Paul Sajna <hello@paulsajna.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250422-b4-qcom-wdt-v3-1-730d4d5a858d@paulsajna.com
Signed-off-by: Casey Connolly <casey.connolly@linaro.org>

configs/qcom_defconfig

@@ -143,3 +143,5 @@ CONFIG_VIDEO_FONT_16X32=y
 CONFIG_SYS_WHITE_ON_BLACK=y
 CONFIG_NO_FB_CLEAR=y
 CONFIG_VIDEO_SIMPLE=y
+CONFIG_WDT_QCOM=y
+CONFIG_WDT=y

drivers/watchdog/Kconfig

@@ -335,6 +335,13 @@ config WDT_K3_RTI_FW_FILE
 
 endif
 
+config WDT_QCOM
+	bool "Qualcomm watchdog timer support"
+	depends on WDT && ARCH_SNAPDRAGON
+	help
+	  Select this to enable Qualcomm watchdog timer, which can be found on
+	  some Qualcomm chips.
+
 config WDT_RENESAS
 	bool "Renesas watchdog timer support"
 	depends on WDT && R8A779F0

drivers/watchdog/Makefile

@@ -55,3 +55,4 @@ obj-$(CONFIG_WDT_SUNXI) += sunxi_wdt.o
 obj-$(CONFIG_WDT_TANGIER) += tangier_wdt.o
 obj-$(CONFIG_WDT_XILINX) += xilinx_wwdt.o
 obj-$(CONFIG_WDT_ADI) += adi_wdt.o
+obj-$(CONFIG_WDT_QCOM) += qcom-wdt.o

drivers/watchdog/qcom-wdt.c

@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2014, The Linux Foundation. All rights reserved.
+ * Copyright (c) Linaro Ltd. 2024
+ *
+ * Authors:
+ *   Casey Connolly <casey.connolly@linaro.org>
+ *   Paul Sajna <hello@paulsajna.com>
+ *
+ * Derived from linux/drivers/watchdog/qcom-wdt.c
+ */
+
+#include <dm.h>
+#include <dm/device_compat.h>
+#include <wdt.h>
+
+#include <asm/io.h>
+
+enum wdt_reg {
+	WDT_RST,
+	WDT_EN,
+	WDT_STS,
+	WDT_BARK_TIME,
+	WDT_BITE_TIME,
+};
+
+struct qcom_wdt_match_data {
+	const u32 *offset;
+};
+
+struct qcom_wdt {
+	void __iomem *base;
+	const u32 *layout;
+};
+
+static const u32 reg_offset_data_kpss[] = {
+	[WDT_RST] = 0x4,
+	[WDT_EN] = 0x8,
+	[WDT_STS] = 0xC,
+	[WDT_BARK_TIME] = 0x10,
+	[WDT_BITE_TIME] = 0x14,
+};
+
+static const struct qcom_wdt_match_data match_data_kpss = {
+	.offset = reg_offset_data_kpss,
+};
+
+static void __iomem *wdt_addr(struct qcom_wdt *wdt, enum wdt_reg reg)
+{
+	return wdt->base + wdt->layout[reg];
+}
+
+int qcom_wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)
+{
+	struct qcom_wdt *wdt = dev_get_priv(dev);
+
+	writel(0, wdt_addr(wdt, WDT_EN));
+	writel(1, wdt_addr(wdt, WDT_RST));
+	writel(1, wdt_addr(wdt, WDT_EN));
+	if (readl(wdt_addr(wdt, WDT_EN)) != 1) {
+		dev_err(dev, "Failed to enable Qualcomm watchdog!\n");
+		return -EIO;
+	}
+	return 0;
+}
+
+int qcom_wdt_stop(struct udevice *dev)
+{
+	struct qcom_wdt *wdt = dev_get_priv(dev);
+
+	writel(0, wdt_addr(wdt, WDT_EN));
+	if (readl(wdt_addr(wdt, WDT_EN))) {
+		dev_err(dev, "Failed to disable Qualcomm watchdog!\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
+int qcom_wdt_reset(struct udevice *dev)
+{
+	struct qcom_wdt *wdt = dev_get_priv(dev);
+
+	writel(1, wdt_addr(wdt, WDT_RST));
+	return 0;
+}
+
+static int qcom_wdt_probe(struct udevice *dev)
+{
+	struct qcom_wdt *wdt = dev_get_priv(dev);
+	struct qcom_wdt_match_data *data = (void *)dev_get_driver_data(dev);
+
+	wdt->base = dev_read_addr_ptr(dev);
+	wdt->layout = data->offset;
+
+	return 0;
+}
+
+static const struct wdt_ops qcom_wdt_ops = {
+	.start = qcom_wdt_start,
+	.stop = qcom_wdt_stop,
+	.reset = qcom_wdt_reset,
+};
+
+static const struct udevice_id qcom_wdt_ids[] = {
+	{ .compatible = "qcom,kpss-wdt", .data = (ulong)&match_data_kpss },
+	{}
+};
+
+U_BOOT_DRIVER(qcom_wdt) = {
+	.name = "qcom_wdt",
+	.id = UCLASS_WDT,
+	.of_match = qcom_wdt_ids,
+	.ops = &qcom_wdt_ops,
+	.probe = qcom_wdt_probe,
+	.priv_auto = sizeof(struct qcom_wdt),
+};