platform/x86: dell-dw5826e: Add reset driver for DW5826e

If the DW5826e is in a frozen state and unable to receive USB commands,
this driver provides a method for the user to reset the DW5826e via ACPI.

E.g: echo 1 > /sys/bus/platform/devices/PALC0001\:00/wwan_reset

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Armin Wolf <W_Armin@gmx.de>
Signed-off-by: Jack Wu <jackbb_wu@compal.com>
Link: https://patch.msgid.link/20260526-dell-reset-v8-v8-1-d3a29cb4cf2f@compal.com
[ij: removed default m]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Documentation/ABI/testing/sysfs-driver-dell-dw5826e-reset

@@ -0,0 +1,9 @@
+What:		/sys/bus/platform/devices/<PALC0001 device>/wwan_reset
+Date:		April 2026
+KernelVersion:	7.2
+Contact:	Jackbb Wu <jackbb.wu@compal.com>
+Description:
+		Writing to this file triggers a Platform Level Device Reset
+		(PLDR) of the Dell DW5826e WWAN module via an ACPI _DSM
+		method. This can be used to recover the modem when it is in
+		a frozen state and unable to respond to USB commands.

drivers/platform/x86/dell/Kconfig

@@ -276,4 +276,9 @@ config DELL_WMI_SYSMAN
 	  To compile this driver as a module, choose M here: the module will
 	  be called dell-wmi-sysman.
 
+config DELL_DW5826E_RESET
+	tristate "Dell DW5826e PLDR reset support"
+	depends on ACPI
+	help
+	  This adds support for the Dell DW5826e PLDR reset via ACPI
 endif # X86_PLATFORM_DRIVERS_DELL

drivers/platform/x86/dell/Makefile

@@ -28,3 +28,4 @@ obj-$(CONFIG_DELL_WMI_DESCRIPTOR)		+= dell-wmi-descriptor.o
 obj-$(CONFIG_DELL_WMI_DDV)			+= dell-wmi-ddv.o
 obj-$(CONFIG_DELL_WMI_LED)			+= dell-wmi-led.o
 obj-$(CONFIG_DELL_WMI_SYSMAN)			+= dell-wmi-sysman/
+obj-$(CONFIG_DELL_DW5826E_RESET)		+= dell-dw5826e-reset.o

drivers/platform/x86/dell/dell-dw5826e-reset.c

@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  dell-dw5826e-reset.c - Dell DW5826e reset driver
+ *
+ *  Copyright (C) 2026 Jackbb Wu <jackbb.wu@compal.com>
+ */
+
+#include <linux/acpi.h>
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+#include <linux/uuid.h>
+
+#define PALC_DSM_FN_TRIGGER_PLDR    BIT(1)
+
+static guid_t palc_dsm_guid =
+	GUID_INIT(0x5a1a4bba, 0x8006, 0x487e, 0xbe, 0x0a, 0xac, 0xf5, 0xd8, 0xfd, 0xfe, 0x59);
+
+static int trigger_palc_pldr(struct device *dev, acpi_handle handle)
+{
+	union acpi_object *obj;
+	int ret = 0;
+
+	obj = acpi_evaluate_dsm(handle, &palc_dsm_guid, 1, PALC_DSM_FN_TRIGGER_PLDR, NULL);
+	if (!obj) {
+		dev_err(dev, "Failed to evaluate _DSM\n");
+		return -EIO;
+	}
+
+	if (obj->type != ACPI_TYPE_BUFFER) {
+		dev_err(dev, "Unexpected _DSM return type: %d\n", obj->type);
+		ret = -EINVAL;
+	}
+
+	ACPI_FREE(obj);
+	return ret;
+}
+
+static ssize_t wwan_reset_store(struct device *dev, struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	acpi_handle handle = ACPI_HANDLE(dev);
+	int ret;
+
+	ret = trigger_palc_pldr(dev, handle);
+	if (ret)
+		return ret;
+
+	return count;
+}
+static DEVICE_ATTR_WO(wwan_reset);
+
+static struct attribute *palc_attrs[] = {
+	&dev_attr_wwan_reset.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(palc);
+
+static int palc_probe(struct platform_device *pdev)
+{
+	acpi_handle handle;
+
+	handle = ACPI_HANDLE(&pdev->dev);
+	if (!handle)
+		return -ENODEV;
+
+	if (!acpi_check_dsm(handle, &palc_dsm_guid, 1, PALC_DSM_FN_TRIGGER_PLDR))
+		return -ENODEV;
+
+	return 0;
+}
+
+static const struct acpi_device_id palc_acpi_ids[] = {
+	{ "PALC0001", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, palc_acpi_ids);
+
+static struct platform_driver palc_driver = {
+	.driver = {
+		.name = "dell-dw5826e-reset",
+		.acpi_match_table = palc_acpi_ids,
+		.dev_groups = palc_groups,
+	},
+	.probe  = palc_probe,
+};
+module_platform_driver(palc_driver);
+
+MODULE_DESCRIPTION("Dell DW5826e reset driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("JackBB Wu");