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 */