power: reset: Add a driver for the ep93xx reset

Implement the reset behaviour of the various EP93xx SoCS
in drivers/power/reset.

It used to be located in arch/arm/mach-ep93xx.

Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Acked-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/power/reset/Kconfig

@@ -75,6 +75,16 @@ config POWER_RESET_BRCMSTB
 	  Say Y here if you have a Broadcom STB board and you wish
 	  to have restart support.
 
+config POWER_RESET_EP93XX
+	bool "Cirrus EP93XX reset driver" if COMPILE_TEST
+	depends on MFD_SYSCON
+	default ARCH_EP93XX
+	help
+	  This driver provides restart support for Cirrus EP93XX SoC.
+
+	  Say Y here if you have a Cirrus EP93XX SoC and you wish
+	  to have restart support.
+
 config POWER_RESET_GEMINI_POWEROFF
 	bool "Cortina Gemini power-off driver"
 	depends on ARCH_GEMINI || COMPILE_TEST

drivers/power/reset/Makefile

@@ -7,6 +7,7 @@ obj-$(CONFIG_POWER_RESET_ATC260X) += atc260x-poweroff.o
 obj-$(CONFIG_POWER_RESET_AXXIA) += axxia-reset.o
 obj-$(CONFIG_POWER_RESET_BRCMKONA) += brcm-kona-reset.o
 obj-$(CONFIG_POWER_RESET_BRCMSTB) += brcmstb-reboot.o
+obj-$(CONFIG_POWER_RESET_EP93XX) += ep93xx-restart.o
 obj-$(CONFIG_POWER_RESET_GEMINI_POWEROFF) += gemini-poweroff.o
 obj-$(CONFIG_POWER_RESET_GPIO) += gpio-poweroff.o
 obj-$(CONFIG_POWER_RESET_GPIO_RESTART) += gpio-restart.o

drivers/power/reset/ep93xx-restart.c

@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Cirrus EP93xx SoC reset driver
+ *
+ * Copyright (C) 2021 Nikita Shubin <nikita.shubin@maquefel.me>
+ */
+
+#include <linux/bits.h>
+#include <linux/container_of.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/notifier.h>
+#include <linux/reboot.h>
+#include <linux/slab.h>
+
+#include <linux/soc/cirrus/ep93xx.h>
+
+#define EP93XX_SYSCON_DEVCFG		0x80
+#define EP93XX_SYSCON_DEVCFG_SWRST	BIT(31)
+
+struct ep93xx_restart {
+	struct ep93xx_regmap_adev *aux_dev;
+	struct notifier_block restart_handler;
+};
+
+static int ep93xx_restart_handle(struct notifier_block *this,
+				 unsigned long mode, void *cmd)
+{
+	struct ep93xx_restart *priv =
+		container_of(this, struct ep93xx_restart, restart_handler);
+	struct ep93xx_regmap_adev *aux = priv->aux_dev;
+
+	/* Issue the reboot */
+	aux->update_bits(aux->map, aux->lock, EP93XX_SYSCON_DEVCFG,
+			 EP93XX_SYSCON_DEVCFG_SWRST, EP93XX_SYSCON_DEVCFG_SWRST);
+	aux->update_bits(aux->map, aux->lock, EP93XX_SYSCON_DEVCFG,
+			 EP93XX_SYSCON_DEVCFG_SWRST, 0);
+
+	return NOTIFY_DONE;
+}
+
+static int ep93xx_reboot_probe(struct auxiliary_device *adev,
+			       const struct auxiliary_device_id *id)
+{
+	struct ep93xx_regmap_adev *rdev = to_ep93xx_regmap_adev(adev);
+	struct device *dev = &adev->dev;
+	struct ep93xx_restart *priv;
+	int err;
+
+	if (!rdev->update_bits)
+		return -ENODEV;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->aux_dev = rdev;
+
+	priv->restart_handler.notifier_call = ep93xx_restart_handle;
+	priv->restart_handler.priority = 128;
+
+	err = register_restart_handler(&priv->restart_handler);
+	if (err)
+		return dev_err_probe(dev, err, "can't register restart notifier\n");
+
+	return 0;
+}
+
+static const struct auxiliary_device_id ep93xx_reboot_ids[] = {
+	{
+		.name = "soc_ep93xx.reset-ep93xx",
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(auxiliary, ep93xx_reboot_ids);
+
+static struct auxiliary_driver ep93xx_reboot_driver = {
+	.probe		= ep93xx_reboot_probe,
+	.id_table	= ep93xx_reboot_ids,
+};
+module_auxiliary_driver(ep93xx_reboot_driver);