hwmon: (sch56xx-common) Add automatic module loading on supported devices

This patch enables the sch56xx-common module to get automatically
loaded on supported machines.
If a machine supports Fujitsu's SCH56XX-based hardware monitoring
solutions, it contains a "Antiope"/" Antiope" dmi onboard device
in case of the sch5627 or a "Theseus"/" Theseus" dmi onboard device
in case of the sch5636.
Since some machines like the Esprimo C700 have a seemingly faulty
DMI table containing both onboard devices, the driver still needs
to probe for the individual superio chip, which in presence of at
least one DMI onboard device however can be considered safe.
Also add a module parameter allowing for bypassing the
DMI check.

Tested on a Fujitsu Esprimo P720.
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20220131211935.3656-3-W_Armin@gmx.deReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/sch56xx-common.c

@@ -7,8 +7,10 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
+#include <linux/mod_devicetable.h>
 #include <linux/init.h>
 #include <linux/platform_device.h>
+#include <linux/dmi.h>
 #include <linux/err.h>
 #include <linux/io.h>
 #include <linux/acpi.h>
@@ -19,7 +21,10 @@
 #include <linux/slab.h>
 #include "sch56xx-common.h"
 
-/* Insmod parameters */
+static bool ignore_dmi;
+module_param(ignore_dmi, bool, 0);
+MODULE_PARM_DESC(ignore_dmi, "Omit DMI check for supported devices (default=0)");
+
 static bool nowayout = WATCHDOG_NOWAYOUT;
 module_param(nowayout, bool, 0);
 MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
@@ -518,11 +523,42 @@ static int __init sch56xx_device_add(int address, const char *name)
 	return PTR_ERR_OR_ZERO(sch56xx_pdev);
 }
 
+/* For autoloading only */
+static const struct dmi_system_id sch56xx_dmi_table[] __initconst = {
+	{
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "FUJITSU"),
+		},
+	},
+	{ }
+};
+MODULE_DEVICE_TABLE(dmi, sch56xx_dmi_table);
+
 static int __init sch56xx_init(void)
 {
-	int address;
 	const char *name = NULL;
+	int address;
 
+	if (!ignore_dmi) {
+		if (!dmi_check_system(sch56xx_dmi_table))
+			return -ENODEV;
+
+		/*
+		 * Some machines like the Esprimo P720 and Esprimo C700 have
+		 * onboard devices named " Antiope"/" Theseus" instead of
+		 * "Antiope"/"Theseus", so we need to check for both.
+		 */
+		if (!dmi_find_device(DMI_DEV_TYPE_OTHER, "Antiope", NULL) &&
+		    !dmi_find_device(DMI_DEV_TYPE_OTHER, " Antiope", NULL) &&
+		    !dmi_find_device(DMI_DEV_TYPE_OTHER, "Theseus", NULL) &&
+		    !dmi_find_device(DMI_DEV_TYPE_OTHER, " Theseus", NULL))
+			return -ENODEV;
+	}
+
+	/*
+	 * Some devices like the Esprimo C700 have both onboard devices,
+	 * so we still have to check manually
+	 */
 	address = sch56xx_find(0x4e, &name);
 	if (address < 0)
 		address = sch56xx_find(0x2e, &name);