soc: nuvoton: Add SoC info driver for WPCM450

Add a SoC information driver for Nuvoton WPCM450 SoCs. It provides
information such as the SoC revision.

Usage example:

  # grep . /sys/devices/soc0/*
  /sys/devices/soc0/family:Nuvoton NPCM
  /sys/devices/soc0/revision:A3
  /sys/devices/soc0/soc_id:WPCM450

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://lore.kernel.org/r/20221031223926.241641-1-j.neuschaefer@gmx.net
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230201051717.1005938-1-joel@jms.id.au
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/soc/Kconfig

@@ -16,6 +16,7 @@ source "drivers/soc/litex/Kconfig"
 source "drivers/soc/loongson/Kconfig"
 source "drivers/soc/mediatek/Kconfig"
 source "drivers/soc/microchip/Kconfig"
+source "drivers/soc/nuvoton/Kconfig"
 source "drivers/soc/pxa/Kconfig"
 source "drivers/soc/qcom/Kconfig"
 source "drivers/soc/renesas/Kconfig"

drivers/soc/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_LITEX_SOC_CONTROLLER) += litex/
 obj-y				+= loongson/
 obj-y				+= mediatek/
 obj-y				+= microchip/
+obj-y				+= nuvoton/
 obj-y				+= pxa/
 obj-y				+= amlogic/
 obj-y				+= qcom/

drivers/soc/nuvoton/Kconfig

@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+menuconfig WPCM450_SOC
+	tristate "Nuvoton WPCM450 SoC driver"
+	default y if ARCH_WPCM450
+	select SOC_BUS
+	help
+	  Say Y here to compile the SoC information driver for Nuvoton
+	  WPCM450 SoCs.
+
+	  This driver provides information such as the SoC model and
+	  revision.

drivers/soc/nuvoton/Makefile

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_WPCM450_SOC)	+= wpcm450-soc.o

drivers/soc/nuvoton/wpcm450-soc.c

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Nuvoton WPCM450 SoC Identification
+ *
+ * Copyright (C) 2022 Jonathan Neuschäfer
+ */
+
+#include <linux/mfd/syscon.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/sys_soc.h>
+
+#define GCR_PDID	0
+#define PDID_CHIP(x)	((x) & 0x00ffffff)
+#define CHIP_WPCM450	0x926450
+#define PDID_REV(x)	((x) >> 24)
+
+struct revision {
+	u8 number;
+	const char *name;
+};
+
+static const struct revision revisions[] __initconst = {
+	{ 0x00, "Z1" },
+	{ 0x03, "Z2" },
+	{ 0x04, "Z21" },
+	{ 0x08, "A1" },
+	{ 0x09, "A2" },
+	{ 0x0a, "A3" },
+	{}
+};
+
+static const char * __init get_revision(unsigned int rev)
+{
+	int i;
+
+	for (i = 0; revisions[i].name; i++)
+		if (revisions[i].number == rev)
+			return revisions[i].name;
+	return NULL;
+}
+
+static struct soc_device_attribute *wpcm450_attr;
+static struct soc_device *wpcm450_soc;
+
+static int __init wpcm450_soc_init(void)
+{
+	struct soc_device_attribute *attr;
+	struct soc_device *soc;
+	const char *revision;
+	struct regmap *gcr;
+	u32 pdid;
+	int ret;
+
+	if (!of_machine_is_compatible("nuvoton,wpcm450"))
+		return 0;
+
+	gcr = syscon_regmap_lookup_by_compatible("nuvoton,wpcm450-gcr");
+	if (IS_ERR(gcr))
+		return PTR_ERR(gcr);
+	ret = regmap_read(gcr, GCR_PDID, &pdid);
+	if (ret)
+		return ret;
+
+	if (PDID_CHIP(pdid) != CHIP_WPCM450) {
+		pr_warn("Unknown chip ID in GCR.PDID: 0x%06x\n", PDID_CHIP(pdid));
+		return -ENODEV;
+	}
+
+	revision = get_revision(PDID_REV(pdid));
+	if (!revision) {
+		pr_warn("Unknown chip revision in GCR.PDID: 0x%02x\n", PDID_REV(pdid));
+		return -ENODEV;
+	}
+
+	attr = kzalloc(sizeof(*attr), GFP_KERNEL);
+	if (!attr)
+		return -ENOMEM;
+
+	attr->family = "Nuvoton NPCM";
+	attr->soc_id = "WPCM450";
+	attr->revision = revision;
+	soc = soc_device_register(attr);
+	if (IS_ERR(soc)) {
+		kfree(attr);
+		pr_warn("Could not register SoC device\n");
+		return PTR_ERR(soc);
+	}
+
+	wpcm450_soc = soc;
+	wpcm450_attr = attr;
+	return 0;
+}
+module_init(wpcm450_soc_init);
+
+static void __exit wpcm450_soc_exit(void)
+{
+	if (wpcm450_soc) {
+		soc_device_unregister(wpcm450_soc);
+		wpcm450_soc = NULL;
+		kfree(wpcm450_attr);
+	}
+}
+module_exit(wpcm450_soc_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jonathan Neuschäfer");
+MODULE_DESCRIPTION("Nuvoton WPCM450 SoC Identification driver");