bus: sunxi-rsb: Add driver for Allwinner Reduced Serial Bus

Reduced Serial Bus (RSB) is an Allwinner proprietery interface
used to communicate with PMICs and other peripheral ICs.

RSB is a two-wire push-pull serial bus that supports 1 master
device and up to 15 active slave devices.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

4 files changed, 900 insertions, 0 deletions

diff --git a/drivers/bus/Kconfig b/drivers/bus/Kconfig
index 1a82f3a17681..78382de19ed9 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -121,6 +121,17 @@ config SIMPLE_PM_BUS
 	  Controller (BSC, sometimes called "LBSC within Bus Bridge", or
 	  "External Bus Interface") as found on several Renesas ARM SoCs.
 
+config SUNXI_RSB
+	tristate "Allwinner sunXi Reduced Serial Bus Driver"
+	  default MACH_SUN8I || MACH_SUN9I
+	  depends on ARCH_SUNXI
+	  select REGMAP
+	  help
+	  Say y here to enable support for Allwinner's Reduced Serial Bus
+	  (RSB) support. This controller is responsible for communicating
+	  with various RSB based devices, such as AXP223, AXP8XX PMICs,
+	  and AC100/AC200 ICs.
+
 config VEXPRESS_CONFIG
 	bool "Versatile Express configuration bus"
 	default y if ARCH_VEXPRESS
diff --git a/drivers/bus/Makefile b/drivers/bus/Makefile
index 790e7b933fb2..fcb9f9794a1f 100644
--- a/drivers/bus/Makefile
+++ b/drivers/bus/Makefile
@@ -15,5 +15,6 @@ obj-$(CONFIG_MVEBU_MBUS) 	+= mvebu-mbus.o
 obj-$(CONFIG_OMAP_INTERCONNECT)	+= omap_l3_smx.o omap_l3_noc.o
 
 obj-$(CONFIG_OMAP_OCP2SCP)	+= omap-ocp2scp.o
+obj-$(CONFIG_SUNXI_RSB)		+= sunxi-rsb.o
 obj-$(CONFIG_SIMPLE_PM_BUS)	+= simple-pm-bus.o
 obj-$(CONFIG_VEXPRESS_CONFIG)	+= vexpress-config.o
diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
new file mode 100644
index 000000000000..846bc29c157d
--- /dev/null
+++ b/drivers/bus/sunxi-rsb.c
@@ -0,0 +1,783 @@
+/*
+ * RSB (Reduced Serial Bus) driver.
+ *
+ * Author: Chen-Yu Tsai <wens@csie.org>
+ *
+ * This file is licensed under the terms of the GNU General Public License
+ * version 2.  This program is licensed "as is" without any warranty of any
+ * kind, whether express or implied.
+ *
+ * The RSB controller looks like an SMBus controller which only supports
+ * byte and word data transfers. But, it differs from standard SMBus
+ * protocol on several aspects:
+ * - it uses addresses set at runtime to address slaves. Runtime addresses
+ *   are sent to slaves using their 12bit hardware addresses. Up to 15
+ *   runtime addresses are available.
+ * - it adds a parity bit every 8bits of data and address for read and
+ *   write accesses; this replaces the ack bit
+ * - only one read access is required to read a byte (instead of a write
+ *   followed by a read access in standard SMBus protocol)
+ * - there's no Ack bit after each read access
+ *
+ * This means this bus cannot be used to interface with standard SMBus
+ * devices. Devices known to support this interface include the AXP223,
+ * AXP809, and AXP806 PMICs, and the AC100 audio codec, all from X-Powers.
+ *
+ * A description of the operation and wire protocol can be found in the
+ * RSB section of Allwinner's A80 user manual, which can be found at
+ *
+ *     https://github.com/allwinner-zh/documents/tree/master/A80
+ *
+ * This document is officially released by Allwinner.
+ *
+ * This driver is based on i2c-sun6i-p2wi.c, the P2WI bus driver.
+ *
+ */
+
+#include <linux/clk.h>
+#include <linux/clk/clk-conf.h>
+#include <linux/device.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+#include <linux/sunxi-rsb.h>
+#include <linux/types.h>
+
+/* RSB registers */
+#define RSB_CTRL	0x0	/* Global control */
+#define RSB_CCR		0x4	/* Clock control */
+#define RSB_INTE	0x8	/* Interrupt controls */
+#define RSB_INTS	0xc	/* Interrupt status */
+#define RSB_ADDR	0x10	/* Address to send with read/write command */
+#define RSB_DATA	0x1c	/* Data to read/write */
+#define RSB_LCR		0x24	/* Line control */
+#define RSB_DMCR	0x28	/* Device mode (init) control */
+#define RSB_CMD		0x2c	/* RSB Command */
+#define RSB_DAR		0x30	/* Device address / runtime address */
+
+/* CTRL fields */
+#define RSB_CTRL_START_TRANS		BIT(7)
+#define RSB_CTRL_ABORT_TRANS		BIT(6)
+#define RSB_CTRL_GLOBAL_INT_ENB		BIT(1)
+#define RSB_CTRL_SOFT_RST		BIT(0)
+
+/* CLK CTRL fields */
+#define RSB_CCR_SDA_OUT_DELAY(v)	(((v) & 0x7) << 8)
+#define RSB_CCR_MAX_CLK_DIV		0xff
+#define RSB_CCR_CLK_DIV(v)		((v) & RSB_CCR_MAX_CLK_DIV)
+
+/* STATUS fields */
+#define RSB_INTS_TRANS_ERR_ACK		BIT(16)
+#define RSB_INTS_TRANS_ERR_DATA_BIT(v)	(((v) >> 8) & 0xf)
+#define RSB_INTS_TRANS_ERR_DATA		GENMASK(11, 8)
+#define RSB_INTS_LOAD_BSY		BIT(2)
+#define RSB_INTS_TRANS_ERR		BIT(1)
+#define RSB_INTS_TRANS_OVER		BIT(0)
+
+/* LINE CTRL fields*/
+#define RSB_LCR_SCL_STATE		BIT(5)
+#define RSB_LCR_SDA_STATE		BIT(4)
+#define RSB_LCR_SCL_CTL			BIT(3)
+#define RSB_LCR_SCL_CTL_EN		BIT(2)
+#define RSB_LCR_SDA_CTL			BIT(1)
+#define RSB_LCR_SDA_CTL_EN		BIT(0)
+
+/* DEVICE MODE CTRL field values */
+#define RSB_DMCR_DEVICE_START		BIT(31)
+#define RSB_DMCR_MODE_DATA		(0x7c << 16)
+#define RSB_DMCR_MODE_REG		(0x3e << 8)
+#define RSB_DMCR_DEV_ADDR		0x00
+
+/* CMD values */
+#define RSB_CMD_RD8			0x8b
+#define RSB_CMD_RD16			0x9c
+#define RSB_CMD_RD32			0xa6
+#define RSB_CMD_WR8			0x4e
+#define RSB_CMD_WR16			0x59
+#define RSB_CMD_WR32			0x63
+#define RSB_CMD_STRA			0xe8
+
+/* DAR fields */
+#define RSB_DAR_RTA(v)			(((v) & 0xff) << 16)
+#define RSB_DAR_DA(v)			((v) & 0xffff)
+
+#define RSB_MAX_FREQ			20000000
+
+#define RSB_CTRL_NAME			"sunxi-rsb"
+
+struct sunxi_rsb_addr_map {
+	u16 hwaddr;
+	u8 rtaddr;
+};
+
+struct sunxi_rsb {
+	struct device *dev;
+	void __iomem *regs;
+	struct clk *clk;
+	struct reset_control *rstc;
+	struct completion complete;
+	struct mutex lock;
+	unsigned int status;
+};
+
+/* bus / slave device related functions */
+static struct bus_type sunxi_rsb_bus;
+
+static int sunxi_rsb_device_match(struct device *dev, struct device_driver *drv)
+{
+	return of_driver_match_device(dev, drv);
+}
+
+static int sunxi_rsb_device_probe(struct device *dev)
+{
+	const struct sunxi_rsb_driver *drv = to_sunxi_rsb_driver(dev->driver);
+	struct sunxi_rsb_device *rdev = to_sunxi_rsb_device(dev);
+	int ret;
+
+	if (!drv->probe)
+		return -ENODEV;
+
+	if (!rdev->irq) {
+		int irq = -ENOENT;
+
+		if (dev->of_node)
+			irq = of_irq_get(dev->of_node, 0);
+
+		if (irq == -EPROBE_DEFER)
+			return irq;
+		if (irq < 0)
+			irq = 0;
+
+		rdev->irq = irq;
+	}
+
+	ret = of_clk_set_defaults(dev->of_node, false);
+	if (ret < 0)
+		return ret;
+
+	return drv->probe(rdev);
+}
+
+static int sunxi_rsb_device_remove(struct device *dev)
+{
+	const struct sunxi_rsb_driver *drv = to_sunxi_rsb_driver(dev->driver);
+
+	return drv->remove(to_sunxi_rsb_device(dev));
+}
+
+static struct bus_type sunxi_rsb_bus = {
+	.name		= RSB_CTRL_NAME,
+	.match		= sunxi_rsb_device_match,
+	.probe		= sunxi_rsb_device_probe,
+	.remove		= sunxi_rsb_device_remove,
+};
+
+static void sunxi_rsb_dev_release(struct device *dev)
+{
+	struct sunxi_rsb_device *rdev = to_sunxi_rsb_device(dev);
+
+	kfree(rdev);
+}
+
+/**
+ * sunxi_rsb_device_create() - allocate and add an RSB device
+ * @rsb:	RSB controller
+ * @node:	RSB slave device node
+ * @hwaddr:	RSB slave hardware address
+ * @rtaddr:	RSB slave runtime address
+ */
+static struct sunxi_rsb_device *sunxi_rsb_device_create(struct sunxi_rsb *rsb,
+		struct device_node *node, u16 hwaddr, u8 rtaddr)
+{
+	int err;
+	struct sunxi_rsb_device *rdev;
+
+	rdev = kzalloc(sizeof(*rdev), GFP_KERNEL);
+	if (!rdev)
+		return ERR_PTR(-ENOMEM);
+
+	rdev->rsb = rsb;
+	rdev->hwaddr = hwaddr;
+	rdev->rtaddr = rtaddr;
+	rdev->dev.bus = &sunxi_rsb_bus;
+	rdev->dev.parent = rsb->dev;
+	rdev->dev.of_node = node;
+	rdev->dev.release = sunxi_rsb_dev_release;
+
+	dev_set_name(&rdev->dev, "%s-%x", RSB_CTRL_NAME, hwaddr);
+
+	err = device_register(&rdev->dev);
+	if (err < 0) {
+		dev_err(&rdev->dev, "Can't add %s, status %d\n",
+			dev_name(&rdev->dev), err);
+		goto err_device_add;
+	}
+
+	dev_dbg(&rdev->dev, "device %s registered\n", dev_name(&rdev->dev));
+
+err_device_add:
+	put_device(&rdev->dev);
+
+	return ERR_PTR(err);
+}
+
+/**
+ * sunxi_rsb_device_unregister(): unregister an RSB device
+ * @rdev:	rsb_device to be removed
+ */
+static void sunxi_rsb_device_unregister(struct sunxi_rsb_device *rdev)
+{
+	device_unregister(&rdev->dev);
+}
+
+static int sunxi_rsb_remove_devices(struct device *dev, void *data)
+{
+	struct sunxi_rsb_device *rdev = to_sunxi_rsb_device(dev);
+
+	if (dev->bus == &sunxi_rsb_bus)
+		sunxi_rsb_device_unregister(rdev);
+
+	return 0;
+}
+
+/**
+ * sunxi_rsb_driver_register() - Register device driver with RSB core
+ * @rdrv:	device driver to be associated with slave-device.
+ *
+ * This API will register the client driver with the RSB framework.
+ * It is typically called from the driver's module-init function.
+ */
+int sunxi_rsb_driver_register(struct sunxi_rsb_driver *rdrv)
+{
+	rdrv->driver.bus = &sunxi_rsb_bus;
+	return driver_register(&rdrv->driver);
+}
+EXPORT_SYMBOL_GPL(sunxi_rsb_driver_register);
+
+/* common code that starts a transfer */
+static int _sunxi_rsb_run_xfer(struct sunxi_rsb *rsb)
+{
+	if (readl(rsb->regs + RSB_CTRL) & RSB_CTRL_START_TRANS) {
+		dev_dbg(rsb->dev, "RSB transfer still in progress\n");
+		return -EBUSY;
+	}
+
+	reinit_completion(&rsb->complete);
+
+	writel(RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR | RSB_INTS_TRANS_OVER,
+	       rsb->regs + RSB_INTE);
+	writel(RSB_CTRL_START_TRANS | RSB_CTRL_GLOBAL_INT_ENB,
+	       rsb->regs + RSB_CTRL);
+
+	if (!wait_for_completion_io_timeout(&rsb->complete,
+					    msecs_to_jiffies(100))) {
+		dev_dbg(rsb->dev, "RSB timeout\n");
+
+		/* abort the transfer */
+		writel(RSB_CTRL_ABORT_TRANS, rsb->regs + RSB_CTRL);
+
+		/* clear any interrupt flags */
+		writel(readl(rsb->regs + RSB_INTS), rsb->regs + RSB_INTS);
+
+		return -ETIMEDOUT;
+	}
+
+	if (rsb->status & RSB_INTS_LOAD_BSY) {
+		dev_dbg(rsb->dev, "RSB busy\n");
+		return -EBUSY;
+	}
+
+	if (rsb->status & RSB_INTS_TRANS_ERR) {
+		if (rsb->status & RSB_INTS_TRANS_ERR_ACK) {
+			dev_dbg(rsb->dev, "RSB slave nack\n");
+			return -EINVAL;
+		}
+
+		if (rsb->status & RSB_INTS_TRANS_ERR_DATA) {
+			dev_dbg(rsb->dev, "RSB transfer data error\n");
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static int sunxi_rsb_read(struct sunxi_rsb *rsb, u8 rtaddr, u8 addr,
+			  u32 *buf, size_t len)
+{
+	u32 cmd;
+	int ret;
+
+	if (!buf)
+		return -EINVAL;
+
+	switch (len) {
+	case 1:
+		cmd = RSB_CMD_RD8;
+		break;
+	case 2:
+		cmd = RSB_CMD_RD16;
+		break;
+	case 4:
+		cmd = RSB_CMD_RD32;
+		break;
+	default:
+		dev_err(rsb->dev, "Invalid access width: %d\n", len);
+		return -EINVAL;
+	}
+
+	mutex_lock(&rsb->lock);
+
+	writel(addr, rsb->regs + RSB_ADDR);
+	writel(RSB_DAR_RTA(rtaddr), rsb->regs + RSB_DAR);
+	writel(cmd, rsb->regs + RSB_CMD);
+
+	ret = _sunxi_rsb_run_xfer(rsb);
+	if (ret)
+		goto out;
+
+	*buf = readl(rsb->regs + RSB_DATA);
+
+	mutex_unlock(&rsb->lock);
+
+out:
+	return ret;
+}
+
+static int sunxi_rsb_write(struct sunxi_rsb *rsb, u8 rtaddr, u8 addr,
+			   const u32 *buf, size_t len)
+{
+	u32 cmd;
+	int ret;
+
+	if (!buf)
+		return -EINVAL;
+
+	switch (len) {
+	case 1:
+		cmd = RSB_CMD_WR8;
+		break;
+	case 2:
+		cmd = RSB_CMD_WR16;
+		break;
+	case 4:
+		cmd = RSB_CMD_WR32;
+		break;
+	default:
+		dev_err(rsb->dev, "Invalid access width: %d\n", len);
+		return -EINVAL;
+	}
+
+	mutex_lock(&rsb->lock);
+
+	writel(addr, rsb->regs + RSB_ADDR);
+	writel(RSB_DAR_RTA(rtaddr), rsb->regs + RSB_DAR);
+	writel(*buf, rsb->regs + RSB_DATA);
+	writel(cmd, rsb->regs + RSB_CMD);
+	ret = _sunxi_rsb_run_xfer(rsb);
+
+	mutex_unlock(&rsb->lock);
+
+	return ret;
+}
+
+/* RSB regmap functions */
+struct sunxi_rsb_ctx {
+	struct sunxi_rsb_device *rdev;
+	int size;
+};
+
+static int regmap_sunxi_rsb_reg_read(void *context, unsigned int reg,
+				     unsigned int *val)
+{
+	struct sunxi_rsb_ctx *ctx = context;
+	struct sunxi_rsb_device *rdev = ctx->rdev;
+
+	if (reg > 0xff)
+		return -EINVAL;
+
+	return sunxi_rsb_read(rdev->rsb, rdev->rtaddr, reg, val, ctx->size);
+}
+
+static int regmap_sunxi_rsb_reg_write(void *context, unsigned int reg,
+				      unsigned int val)
+{
+	struct sunxi_rsb_ctx *ctx = context;
+	struct sunxi_rsb_device *rdev = ctx->rdev;
+
+	return sunxi_rsb_write(rdev->rsb, rdev->rtaddr, reg, &val, ctx->size);
+}
+
+static void regmap_sunxi_rsb_free_ctx(void *context)
+{
+	struct sunxi_rsb_ctx *ctx = context;
+
+	kfree(ctx);
+}
+
+static struct regmap_bus regmap_sunxi_rsb = {
+	.reg_write = regmap_sunxi_rsb_reg_write,
+	.reg_read = regmap_sunxi_rsb_reg_read,
+	.free_context = regmap_sunxi_rsb_free_ctx,
+	.reg_format_endian_default = REGMAP_ENDIAN_NATIVE,
+	.val_format_endian_default = REGMAP_ENDIAN_NATIVE,
+};
+
+static struct sunxi_rsb_ctx *regmap_sunxi_rsb_init_ctx(struct sunxi_rsb_device *rdev,
+		const struct regmap_config *config)
+{
+	struct sunxi_rsb_ctx *ctx;
+
+	switch (config->val_bits) {
+	case 8:
+	case 16:
+	case 32:
+		break;
+	default:
+		return ERR_PTR(-EINVAL);
+	}
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	ctx->rdev = rdev;
+	ctx->size = config->val_bits / 8;
+
+	return ctx;
+}
+
+struct regmap *__devm_regmap_init_sunxi_rsb(struct sunxi_rsb_device *rdev,
+					    const struct regmap_config *config,
+					    struct lock_class_key *lock_key,
+					    const char *lock_name)
+{
+	struct sunxi_rsb_ctx *ctx = regmap_sunxi_rsb_init_ctx(rdev, config);
+
+	if (IS_ERR(ctx))
+		return ERR_CAST(ctx);
+
+	return __devm_regmap_init(&rdev->dev, &regmap_sunxi_rsb, ctx, config,
+				  lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_sunxi_rsb);
+
+/* RSB controller driver functions */
+static irqreturn_t sunxi_rsb_irq(int irq, void *dev_id)
+{
+	struct sunxi_rsb *rsb = dev_id;
+	u32 status;
+
+	status = readl(rsb->regs + RSB_INTS);
+	rsb->status = status;
+
+	/* Clear interrupts */
+	status &= (RSB_INTS_LOAD_BSY | RSB_INTS_TRANS_ERR |
+		   RSB_INTS_TRANS_OVER);
+	writel(status, rsb->regs + RSB_INTS);
+
+	complete(&rsb->complete);
+
+	return IRQ_HANDLED;
+}
+
+static int sunxi_rsb_init_device_mode(struct sunxi_rsb *rsb)
+{
+	int ret = 0;
+	u32 reg;
+
+	/* send init sequence */
+	writel(RSB_DMCR_DEVICE_START | RSB_DMCR_MODE_DATA |
+	       RSB_DMCR_MODE_REG | RSB_DMCR_DEV_ADDR, rsb->regs + RSB_DMCR);
+
+	readl_poll_timeout(rsb->regs + RSB_DMCR, reg,
+			   !(reg & RSB_DMCR_DEVICE_START), 100, 250000);
+	if (reg & RSB_DMCR_DEVICE_START)
+		ret = -ETIMEDOUT;
+
+	/* clear interrupt status bits */
+	writel(readl(rsb->regs + RSB_INTS), rsb->regs + RSB_INTS);
+
+	return ret;
+}
+
+/*
+ * There are 15 valid runtime addresses, though Allwinner typically
+ * skips the first, for unknown reasons, and uses the following three.
+ *
+ * 0x17, 0x2d, 0x3a, 0x4e, 0x59, 0x63, 0x74, 0x8b,
+ * 0x9c, 0xa6, 0xb1, 0xc5, 0xd2, 0xe8, 0xff
+ *
+ * No designs with 2 RSB slave devices sharing identical hardware
+ * addresses on the same bus have been seen in the wild. All designs
+ * use 0x2d for the primary PMIC, 0x3a for the secondary PMIC if
+ * there is one, and 0x45 for peripheral ICs.
+ *
+ * The hardware does not seem to support re-setting runtime addresses.
+ * Attempts to do so result in the slave devices returning a NACK.
+ * Hence we just hardcode the mapping here, like Allwinner does.
+ */
+
+static const struct sunxi_rsb_addr_map sunxi_rsb_addr_maps[] = {
+	{ 0x3e3, 0x2d }, /* Primary PMIC: AXP223, AXP809, AXP81X, ... */
+	{ 0x745, 0x3a }, /* Secondary PMIC: AXP806, ... */
+	{ 0xe89, 0x45 }, /* Peripheral IC: AC100, ... */
+};
+
+static u8 sunxi_rsb_get_rtaddr(u16 hwaddr)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(sunxi_rsb_addr_maps); i++)
+		if (hwaddr == sunxi_rsb_addr_maps[i].hwaddr)
+			return sunxi_rsb_addr_maps[i].rtaddr;
+
+	return 0; /* 0 is an invalid runtime address */
+}
+
+static int of_rsb_register_devices(struct sunxi_rsb *rsb)
+{
+	struct device *dev = rsb->dev;
+	struct device_node *child, *np = dev->of_node;
+	u32 hwaddr;
+	u8 rtaddr;
+	int ret;
+
+	if (!np)
+		return -EINVAL;
+
+	/* Runtime addresses for all slaves should be set first */
+	for_each_available_child_of_node(np, child) {
+		dev_dbg(dev, "setting child %s runtime address\n",
+			child->full_name);
+
+		ret = of_property_read_u32(child, "reg", &hwaddr);
+		if (ret) {
+			dev_err(dev, "%s: invalid 'reg' property: %d\n",
+				child->full_name, ret);
+			continue;
+		}
+
+		rtaddr = sunxi_rsb_get_rtaddr(hwaddr);
+		if (!rtaddr) {
+			dev_err(dev, "%s: unknown hardware device address\n",
+				child->full_name);
+			continue;
+		}
+
+		/*
+		 * Since no devices have been registered yet, we are the
+		 * only ones using the bus, we can skip locking the bus.
+		 */
+
+		/* setup command parameters */
+		writel(RSB_CMD_STRA, rsb->regs + RSB_CMD);
+		writel(RSB_DAR_RTA(rtaddr) | RSB_DAR_DA(hwaddr),
+		       rsb->regs + RSB_DAR);
+
+		/* send command */
+		ret = _sunxi_rsb_run_xfer(rsb);
+		if (ret)
+			dev_warn(dev, "%s: set runtime address failed: %d\n",
+				 child->full_name, ret);
+	}
+
+	/* Then we start adding devices and probing them */
+	for_each_available_child_of_node(np, child) {
+		struct sunxi_rsb_device *rdev;
+
+		dev_dbg(dev, "adding child %s\n", child->full_name);
+
+		ret = of_property_read_u32(child, "reg", &hwaddr);
+		if (ret)
+			continue;
+
+		rtaddr = sunxi_rsb_get_rtaddr(hwaddr);
+		if (!rtaddr)
+			continue;
+
+		rdev = sunxi_rsb_device_create(rsb, child, hwaddr, rtaddr);
+		if (IS_ERR(rdev))
+			dev_err(dev, "failed to add child device %s: %ld\n",
+				child->full_name, PTR_ERR(rdev));
+	}
+
+	return 0;
+}
+
+static const struct of_device_id sunxi_rsb_of_match_table[] = {
+	{ .compatible = "allwinner,sun8i-a23-rsb" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, sunxi_rsb_of_match_table);
+
+static int sunxi_rsb_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct resource *r;
+	struct sunxi_rsb *rsb;
+	unsigned long p_clk_freq;
+	u32 clk_delay, clk_freq = 3000000;
+	int clk_div, irq, ret;
+	u32 reg;
+
+	of_property_read_u32(np, "clock-frequency", &clk_freq);
+	if (clk_freq > RSB_MAX_FREQ) {
+		dev_err(dev,
+			"clock-frequency (%u Hz) is too high (max = 20MHz)\n",
+			clk_freq);
+		return -EINVAL;
+	}
+
+	rsb = devm_kzalloc(dev, sizeof(*rsb), GFP_KERNEL);
+	if (!rsb)
+		return -ENOMEM;
+
+	rsb->dev = dev;
+	platform_set_drvdata(pdev, rsb);
+	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	rsb->regs = devm_ioremap_resource(dev, r);
+	if (IS_ERR(rsb->regs))
+		return PTR_ERR(rsb->regs);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0) {
+		dev_err(dev, "failed to retrieve irq: %d\n", irq);
+		return irq;
+	}
+
+	rsb->clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(rsb->clk)) {
+		ret = PTR_ERR(rsb->clk);
+		dev_err(dev, "failed to retrieve clk: %d\n", ret);
+		return ret;
+	}
+
+	ret = clk_prepare_enable(rsb->clk);
+	if (ret) {
+		dev_err(dev, "failed to enable clk: %d\n", ret);
+		return ret;
+	}
+
+	p_clk_freq = clk_get_rate(rsb->clk);
+
+	rsb->rstc = devm_reset_control_get(dev, NULL);
+	if (IS_ERR(rsb->rstc)) {
+		ret = PTR_ERR(rsb->rstc);
+		dev_err(dev, "failed to retrieve reset controller: %d\n", ret);
+		goto err_clk_disable;
+	}
+
+	ret = reset_control_deassert(rsb->rstc);
+	if (ret) {
+		dev_err(dev, "failed to deassert reset line: %d\n", ret);
+		goto err_clk_disable;
+	}
+
+	init_completion(&rsb->complete);
+	mutex_init(&rsb->lock);
+
+	/* reset the controller */
+	writel(RSB_CTRL_SOFT_RST, rsb->regs + RSB_CTRL);
+	readl_poll_timeout(rsb->regs + RSB_CTRL, reg,
+			   !(reg & RSB_CTRL_SOFT_RST), 1000, 100000);
+
+	/*
+	 * Clock frequency and delay calculation code is from
+	 * Allwinner U-boot sources.
+	 *
+	 * From A83 user manual:
+	 * bus clock frequency = parent clock frequency / (2 * (divider + 1))
+	 */
+	clk_div = p_clk_freq / clk_freq / 2;
+	if (!clk_div)
+		clk_div = 1;
+	else if (clk_div > RSB_CCR_MAX_CLK_DIV + 1)
+		clk_div = RSB_CCR_MAX_CLK_DIV + 1;
+
+	clk_delay = clk_div >> 1;
+	if (!clk_delay)
+		clk_delay = 1;
+
+	dev_info(dev, "RSB running at %lu Hz\n", p_clk_freq / clk_div / 2);
+	writel(RSB_CCR_SDA_OUT_DELAY(clk_delay) | RSB_CCR_CLK_DIV(clk_div - 1),
+	       rsb->regs + RSB_CCR);
+
+	ret = devm_request_irq(dev, irq, sunxi_rsb_irq, 0, RSB_CTRL_NAME, rsb);
+	if (ret) {
+		dev_err(dev, "can't register interrupt handler irq %d: %d\n",
+			irq, ret);
+		goto err_reset_assert;
+	}
+
+	/* initialize all devices on the bus into RSB mode */
+	ret = sunxi_rsb_init_device_mode(rsb);
+	if (ret)
+		dev_warn(dev, "Initialize device mode failed: %d\n", ret);
+
+	of_rsb_register_devices(rsb);
+
+	return 0;
+
+err_reset_assert:
+	reset_control_assert(rsb->rstc);
+
+err_clk_disable:
+	clk_disable_unprepare(rsb->clk);
+
+	return ret;
+}
+
+static int sunxi_rsb_remove(struct platform_device *pdev)
+{
+	struct sunxi_rsb *rsb = platform_get_drvdata(pdev);
+
+	device_for_each_child(rsb->dev, NULL, sunxi_rsb_remove_devices);
+	reset_control_assert(rsb->rstc);
+	clk_disable_unprepare(rsb->clk);
+
+	return 0;
+}
+
+static struct platform_driver sunxi_rsb_driver = {
+	.probe = sunxi_rsb_probe,
+	.remove	= sunxi_rsb_remove,
+	.driver	= {
+		.name = RSB_CTRL_NAME,
+		.of_match_table = sunxi_rsb_of_match_table,
+	},
+};
+
+static int __init sunxi_rsb_init(void)
+{
+	int ret;
+
+	ret = bus_register(&sunxi_rsb_bus);
+	if (ret) {
+		pr_err("failed to register sunxi sunxi_rsb bus: %d\n", ret);
+		return ret;
+	}
+
+	return platform_driver_register(&sunxi_rsb_driver);
+}
+module_init(sunxi_rsb_init);
+
+static void __exit sunxi_rsb_exit(void)
+{
+	platform_driver_unregister(&sunxi_rsb_driver);
+	bus_unregister(&sunxi_rsb_bus);
+}
+module_exit(sunxi_rsb_exit);
+
+MODULE_AUTHOR("Chen-Yu Tsai <wens@csie.org>");
+MODULE_DESCRIPTION("Allwinner sunXi Reduced Serial Bus controller driver");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/sunxi-rsb.h b/include/linux/sunxi-rsb.h
new file mode 100644
index 000000000000..7e75bb0346d0
--- /dev/null
+++ b/include/linux/sunxi-rsb.h
@@ -0,0 +1,105 @@
+/*
+ * Allwinner Reduced Serial Bus Driver
+ *
+ * Copyright (c) 2015 Chen-Yu Tsai
+ *
+ * Author: Chen-Yu Tsai <wens@csie.org>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2.  This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+#ifndef _SUNXI_RSB_H
+#define _SUNXI_RSB_H
+
+#include <linux/device.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+
+struct sunxi_rsb;
+
+/**
+ * struct sunxi_rsb_device - Basic representation of an RSB device
+ * @dev:	Driver model representation of the device.
+ * @ctrl:	RSB controller managing the bus hosting this device.
+ * @rtaddr:	This device's runtime address
+ * @hwaddr:	This device's hardware address
+ */
+struct sunxi_rsb_device {
+	struct device		dev;
+	struct sunxi_rsb	*rsb;
+	int			irq;
+	u8			rtaddr;
+	u16			hwaddr;
+};
+
+static inline struct sunxi_rsb_device *to_sunxi_rsb_device(struct device *d)
+{
+	return container_of(d, struct sunxi_rsb_device, dev);
+}
+
+static inline void *sunxi_rsb_device_get_drvdata(const struct sunxi_rsb_device *rdev)
+{
+	return dev_get_drvdata(&rdev->dev);
+}
+
+static inline void sunxi_rsb_device_set_drvdata(struct sunxi_rsb_device *rdev,
+						void *data)
+{
+	dev_set_drvdata(&rdev->dev, data);
+}
+
+/**
+ * struct sunxi_rsb_driver - RSB slave device driver
+ * @driver:	RSB device drivers should initialize name and owner field of
+ *		this structure.
+ * @probe:	binds this driver to a RSB device.
+ * @remove:	unbinds this driver from the RSB device.
+ */
+struct sunxi_rsb_driver {
+	struct device_driver driver;
+	int (*probe)(struct sunxi_rsb_device *rdev);
+	int (*remove)(struct sunxi_rsb_device *rdev);
+};
+
+static inline struct sunxi_rsb_driver *to_sunxi_rsb_driver(struct device_driver *d)
+{
+	return container_of(d, struct sunxi_rsb_driver, driver);
+}
+
+int sunxi_rsb_driver_register(struct sunxi_rsb_driver *rdrv);
+
+/**
+ * sunxi_rsb_driver_unregister() - unregister an RSB client driver
+ * @rdrv:	the driver to unregister
+ */
+static inline void sunxi_rsb_driver_unregister(struct sunxi_rsb_driver *rdrv)
+{
+	if (rdrv)
+		driver_unregister(&rdrv->driver);
+}
+
+#define module_sunxi_rsb_driver(__sunxi_rsb_driver) \
+	module_driver(__sunxi_rsb_driver, sunxi_rsb_driver_register, \
+			sunxi_rsb_driver_unregister)
+
+struct regmap *__devm_regmap_init_sunxi_rsb(struct sunxi_rsb_device *rdev,
+					    const struct regmap_config *config,
+					    struct lock_class_key *lock_key,
+					    const char *lock_name);
+
+/**
+ * devm_regmap_init_sunxi_rsb(): Initialise managed register map
+ *
+ * @rdev: Device that will be interacted with
+ * @config: Configuration for register map
+ *
+ * The return value will be an ERR_PTR() on error or a valid pointer
+ * to a struct regmap.  The regmap will be automatically freed by the
+ * device management code.
+ */
+#define devm_regmap_init_sunxi_rsb(rdev, config)			\
+	__regmap_lockdep_wrapper(__devm_regmap_init_sunxi_rsb, #config,	\
+				 rdev, config)
+
+#endif /* _SUNXI_RSB_H */