[PATCH v2 1/4] i2c: sunxi: Add Reduced Serial Bus (RSB) support

[Chen-Yu Tsai]

The RSB controller looks like an SMBus controller which only supports byte
and word data transfers. It can also do double-word data transfers, but the
I2C subsystem does not support this, nor have we seen devices using this.

The RSB 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 (known devices supporting this interface are the AXP223, AXP806,
AXP809 PMICs and the AC100 codec/RTC). However the RSB protocol is an
extension of P2WI, which was close enough to SMBus to be integrated into
the I2C subsystem in commit 3e833490fae5 ("i2c: sunxi: add P2WI (Push/Pull
2 Wire Interface) controller support").

Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx>
---
 drivers/i2c/busses/Kconfig         |  12 +
 drivers/i2c/busses/Makefile        |   1 +
 drivers/i2c/busses/i2c-sunxi-rsb.c | 458 +++++++++++++++++++++++++++++++++++++
 3 files changed, 471 insertions(+)
 create mode 100644 drivers/i2c/busses/i2c-sunxi-rsb.c

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 22da9c2ffa22..cf9337877181 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -840,6 +840,18 @@ config I2C_SUN6I_P2WI
 	  This interface is used to connect to specific PMIC devices (like the
 	  AXP221).
 
+config I2C_SUNXI_RSB
+	tristate "Allwinner Reduced Serial Bus controller"
+	depends on RESET_CONTROLLER
+	depends on MACH_SUN8I || MACH_SUN9I || COMPILE_TEST
+	help
+	  If you say yes to this option, support will be included for the
+	  Reduced Serial Bus controller embedded in some sunxi SOCs.
+	  The RSB looks like an SMBus controller (which supports only byte
+	  accesses), but requires setting runtime addresses for slave devices.
+	  This interface is used to connect to specific PMIC devices (like the
+	  AXP223) or peripherals (like the AC100).
+
 config I2C_TEGRA
 	tristate "NVIDIA Tegra internal I2C controller"
 	depends on ARCH_TEGRA
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index 3638feb6677e..f95d50315003 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -81,6 +81,7 @@ obj-$(CONFIG_I2C_SIRF)		+= i2c-sirf.o
 obj-$(CONFIG_I2C_ST)		+= i2c-st.o
 obj-$(CONFIG_I2C_STU300)	+= i2c-stu300.o
 obj-$(CONFIG_I2C_SUN6I_P2WI)	+= i2c-sun6i-p2wi.o
+obj-$(CONFIG_I2C_SUNXI_RSB)	+= i2c-sunxi-rsb.o
 obj-$(CONFIG_I2C_TEGRA)		+= i2c-tegra.o
 obj-$(CONFIG_I2C_VERSATILE)	+= i2c-versatile.o
 obj-$(CONFIG_I2C_WMT)		+= i2c-wmt.o
diff --git a/drivers/i2c/busses/i2c-sunxi-rsb.c b/drivers/i2c/busses/i2c-sunxi-rsb.c
new file mode 100644
index 000000000000..7e9be3e14b8a
--- /dev/null
+++ b/drivers/i2c/busses/i2c-sunxi-rsb.c
@@ -0,0 +1,458 @@
+/*
+ * RSB (Reduced Serial Bus) driver.
+ *
+ * Author: Chen-Yu Tsai <wens@xxxxxxxx>
+ *
+ * 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/i2c.h>
+#include <linux/io.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reset.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_ID(v)	(((v) >> 8) & 0xf)
+#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 rsb {
+	struct i2c_adapter adapter;
+	struct completion complete;
+	unsigned int status;
+	void __iomem *regs;
+	struct clk *clk;
+	struct reset_control *rstc;
+};
+
+static irqreturn_t rsb_interrupt(int irq, void *dev_id)
+{
+	struct rsb *rsb = dev_id;
+	unsigned long 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;
+}
+
+/* common code that starts a transfer */
+static int rsb_run_xfer(struct rsb *rsb)
+{
+	if (readl(rsb->regs + RSB_CTRL) & RSB_CTRL_START_TRANS) {
+		dev_dbg(&rsb->adapter.dev, "RSB bus busy\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);
+
+	wait_for_completion(&rsb->complete);
+
+	if (rsb->status & RSB_INTS_LOAD_BSY) {
+		dev_dbg(&rsb->adapter.dev, "RSB bus busy\n");
+		return -EBUSY;
+	}
+
+	if (rsb->status & RSB_INTS_TRANS_ERR) {
+		dev_dbg(&rsb->adapter.dev, "RSB bus xfer error\n");
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+static int rsb_smbus_xfer(struct i2c_adapter *adap, u16 addr,
+			   unsigned short flags, char read_write,
+			   u8 command, int size, union i2c_smbus_data *data)
+{
+	struct rsb *rsb = i2c_get_adapdata(adap);
+	int ret;
+
+	if (!data)
+		return -EINVAL;
+
+	writel(command, rsb->regs + RSB_ADDR);
+	writel(RSB_DAR_RTA(addr), rsb->regs + RSB_DAR);
+
+	if (read_write == I2C_SMBUS_READ) {
+		if (size == I2C_SMBUS_BYTE_DATA)
+			writel(RSB_CMD_RD8, rsb->regs + RSB_CMD);
+		else
+			writel(RSB_CMD_RD16, rsb->regs + RSB_CMD);
+	} else {
+		if (size == I2C_SMBUS_BYTE_DATA) {
+			writel(RSB_CMD_WR8, rsb->regs + RSB_CMD);
+			writel(data->byte, rsb->regs + RSB_DATA);
+		} else {
+			writel(RSB_CMD_WR16, rsb->regs + RSB_CMD);
+			writel(data->word, rsb->regs + RSB_DATA);
+		}
+	}
+
+	ret = rsb_run_xfer(rsb);
+	if (ret)
+		return ret;
+
+	if (read_write == I2C_SMBUS_READ) {
+		if (size == I2C_SMBUS_BYTE_DATA)
+			data->byte = readl(rsb->regs + RSB_DATA);
+		else
+			data->word = readl(rsb->regs + RSB_DATA);
+	}
+
+	return 0;
+}
+
+static u32 rsb_functionality(struct i2c_adapter *adap)
+{
+	return I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA;
+}
+
+static const struct i2c_algorithm rsb_algo = {
+	.smbus_xfer	= rsb_smbus_xfer,
+	.functionality	= rsb_functionality,
+};
+
+/* following functions are used strictly during device probe */
+static void rsb_init_device_mode(struct rsb *rsb)
+{
+	unsigned long expire = jiffies + msecs_to_jiffies(250);
+	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);
+	do {
+		reg = readl(rsb->regs + RSB_DMCR);
+	} while (time_before(jiffies, expire) && (reg & RSB_DMCR_DEVICE_START));
+
+	if (reg & RSB_DMCR_DEVICE_START)
+		dev_warn(&rsb->adapter.dev, "send init sequence timeout\n");
+
+	/* clear interrupt status bits */
+	writel(readl(rsb->regs + RSB_INTS), rsb->regs + RSB_INTS);
+}
+
+/* 15 valid runtime addresses for RSB slaves */
+static const u8 rsb_valid_rtaddr[] = {
+	0x17, 0x2d, 0x3a, 0x4e, 0x59, 0x63, 0x74,
+	/*
+	 * Currently this driver only supports 7-bit addresses.
+	 * The following addresses will be blocked by the i2c core.
+	 */
+	0x8b, 0x9c, 0xa6, 0xb1, 0xc5, 0xd2, 0xe8, 0xff,
+};
+
+static int rsb_check_rt_addr(u8 addr)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(rsb_valid_rtaddr); i++)
+		if (addr == rsb_valid_rtaddr[i])
+			return 0;
+
+	return -EINVAL;
+}
+
+/* Scan the device tree for child nodes and set runtime address for them. */
+static int rsb_set_rt_addrs(struct rsb *rsb)
+{
+	struct device *dev = rsb->adapter.dev.parent;
+	struct device_node *child, *np = dev->of_node;
+	u32 rt_addr, hw_addr;
+	int ret;
+
+	if (!np)
+		return -EINVAL;
+
+	for_each_child_of_node(np, child) {
+		/* get hardware address */
+		ret = of_property_read_u32(child, "allwinner,rsb-hw-addr",
+					   &hw_addr);
+		if (ret) {
+			dev_warn(dev, "runtime address not given for %s\n",
+				 of_node_full_name(child));
+			continue;
+		}
+
+		/* get runtime address */
+		ret = of_property_read_u32(child, "reg", &rt_addr);
+		if (ret) {
+			dev_warn(dev, "runtime address not given for %s\n",
+				 of_node_full_name(child));
+			continue;
+		}
+
+		/* check runtime address */
+		ret = rsb_check_rt_addr(rt_addr);
+		if (ret) {
+			dev_warn(dev, "runtime address for %s is invalid\n",
+				 of_node_full_name(child));
+			continue;
+		}
+
+		/* setup command parameters */
+		writel(RSB_CMD_STRA, rsb->regs + RSB_CMD);
+		writel(RSB_DAR_RTA(rt_addr) | RSB_DAR_DA(hw_addr),
+		       rsb->regs + RSB_DAR);
+
+		/* send command */
+		ret = rsb_run_xfer(rsb);
+		if (ret)
+			dev_warn(dev, "set runtime address failed for %s\n",
+				 of_node_full_name(child));
+	}
+
+	return 0;
+}
+
+
+static const struct of_device_id rsb_of_match_table[] = {
+	{ .compatible = "allwinner,sun8i-a23-rsb" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, rsb_of_match_table);
+
+static int rsb_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	unsigned long parent_clk_freq;
+	u32 clk_freq = 100000;
+	struct resource *r;
+	struct rsb *rsb;
+	int clk_div;
+	int irq;
+	int ret;
+
+	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)",
+			clk_freq);
+		return -EINVAL;
+	}
+
+	rsb = devm_kzalloc(dev, sizeof(struct rsb), GFP_KERNEL);
+	if (!rsb)
+		return -ENOMEM;
+
+	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);
+
+	strlcpy(rsb->adapter.name, pdev->name, sizeof(rsb->adapter.name));
+	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;
+	}
+
+	parent_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);
+	strlcpy(rsb->adapter.name, RSB_CTRL_NAME, sizeof(rsb->adapter.name));
+	rsb->adapter.dev.parent = dev;
+	rsb->adapter.algo = &rsb_algo;
+	rsb->adapter.owner = THIS_MODULE;
+	rsb->adapter.dev.of_node = pdev->dev.of_node;
+	platform_set_drvdata(pdev, rsb);
+	i2c_set_adapdata(&rsb->adapter, rsb);
+
+	writel(RSB_CTRL_SOFT_RST, rsb->regs + RSB_CTRL);
+
+	clk_div = parent_clk_freq / clk_freq;
+	if (!clk_div) {
+		dev_warn(dev,
+			 "clock-frequency is too high, setting it to %lu Hz\n",
+			 parent_clk_freq);
+		clk_div = 1;
+	} else if (clk_div > RSB_CCR_MAX_CLK_DIV) {
+		dev_warn(dev,
+			 "clock-frequency is too low, setting it to %lu Hz\n",
+			 parent_clk_freq / RSB_CCR_MAX_CLK_DIV);
+		clk_div = RSB_CCR_MAX_CLK_DIV;
+	}
+
+	writel(RSB_CCR_SDA_OUT_DELAY(1) | RSB_CCR_CLK_DIV(clk_div),
+	       rsb->regs + RSB_CCR);
+
+	ret = devm_request_irq(dev, irq, rsb_interrupt, 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;
+	}
+
+	rsb_init_device_mode(rsb);
+
+	ret = rsb_set_rt_addrs(rsb);
+	if (ret)
+		goto err_reset_assert;
+
+	ret = i2c_add_adapter(&rsb->adapter);
+	if (!ret)
+		return 0;
+
+err_reset_assert:
+	reset_control_assert(rsb->rstc);
+
+err_clk_disable:
+	clk_disable_unprepare(rsb->clk);
+
+	return ret;
+}
+
+static int rsb_remove(struct platform_device *dev)
+{
+	struct rsb *rsb = platform_get_drvdata(dev);
+
+	i2c_del_adapter(&rsb->adapter);
+	reset_control_assert(rsb->rstc);
+	clk_disable_unprepare(rsb->clk);
+
+	return 0;
+}
+
+static struct platform_driver rsb_driver = {
+	.probe = rsb_probe,
+	.remove	= rsb_remove,
+	.driver	= {
+		.name = "i2c-sunxi-rsb",
+		.of_match_table = rsb_of_match_table,
+	},
+};
+module_platform_driver(rsb_driver);
+
+MODULE_AUTHOR("Chen-Yu Tsai <wens@xxxxxxxx>");
+MODULE_DESCRIPTION("Allwinner RSB driver");
+MODULE_LICENSE("GPL v2");
-- 
2.1.4

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