i2c: mt7621: Add MediaTek MT7621/7628/7688 I2C driver

This patch adds a driver for the I2C controller found on the MediaTek
MT7621/7628/7688 SoC's. The base version of this driver was done by
Steven Liu (according to the copyright and MODULE_AUTHOR lines). It
can be found in the OpenWRT repositories (v4.14 at the time I looked).

The base driver had many issues, which are disccussed here:

https://en.forum.labs.mediatek.com/t/openwrt-15-05-loads-non-working-i2c-kernel-module-for-mt7688/1286/3

>From this link an enhanced driver version (complete rewrite, mayor
changes: support clock stretching, repeated start, ACK handling and
unlimited message length) from Jan Breuer can be found here:

https://gist.github.com/j123b567/9b555b635c2b4069d716b24198546954

This patch now adds this enhanced I2C driver to mainline.

Changes by Stefan Roese for upstreaming:
- Add devicetree bindings
- checkpatch clean
- Use module_platform_driver()
- Minor cosmetic enhancements
- Removed IO warpped functions
- Use readl_relaxed_poll_timeout() and drop poll_down_timeout()
- Removed superfluous barrier() in mtk_i2c_reset()
- Use i2c_8bit_addr_from_msg()
- Added I2C_FUNC_PROTOCOL_MANGLING
- Removed adap->class = I2C_CLASS_HWMON | I2C_CLASS_SPD;

Signed-off-by: Stefan Roese <sr@denx.de>
Tested-by: René van Dorst <opensource@vdorst.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

MAINTAINERS

@@ -9944,6 +9944,13 @@ L:	linux-wireless@vger.kernel.org
 S:	Maintained
 F:	drivers/net/wireless/mediatek/mt7601u/
 
+MEDIATEK MT7621/28/88 I2C DRIVER
+M:	Stefan Roese <sr@denx.de>
+L:	linux-i2c@vger.kernel.org
+S:	Maintained
+F:	drivers/i2c/busses/i2c-mt7621.c
+F:	Documentation/devicetree/bindings/i2c/i2c-mt7621.txt
+
 MEDIATEK NAND CONTROLLER DRIVER
 M:	Xiaolei Li <xiaolei.li@mediatek.com>
 L:	linux-mtd@lists.infradead.org

drivers/i2c/busses/Kconfig

@@ -747,6 +747,13 @@ config I2C_MT65XX
 	  If you want to use MediaTek(R) I2C interface, say Y or M here.
 	  If unsure, say N.
 
+config I2C_MT7621
+	tristate "MT7621/MT7628 I2C Controller"
+	depends on (RALINK && (SOC_MT7620 || SOC_MT7621)) || COMPILE_TEST
+	help
+	  Say Y here to include support for I2C controller in the
+	  MediaTek MT7621/MT7628 SoCs.
+
 config I2C_MV64XXX
 	tristate "Marvell mv64xxx I2C Controller"
 	depends on MV64X60 || PLAT_ORION || ARCH_SUNXI || ARCH_MVEBU

drivers/i2c/busses/Makefile

@@ -77,6 +77,7 @@ obj-$(CONFIG_I2C_LPC2K)		+= i2c-lpc2k.o
 obj-$(CONFIG_I2C_MESON)		+= i2c-meson.o
 obj-$(CONFIG_I2C_MPC)		+= i2c-mpc.o
 obj-$(CONFIG_I2C_MT65XX)	+= i2c-mt65xx.o
+obj-$(CONFIG_I2C_MT7621)	+= i2c-mt7621.o
 obj-$(CONFIG_I2C_MV64XXX)	+= i2c-mv64xxx.o
 obj-$(CONFIG_I2C_MXS)		+= i2c-mxs.o
 obj-$(CONFIG_I2C_NOMADIK)	+= i2c-nomadik.o

drivers/i2c/busses/i2c-mt7621.c

@@ -0,0 +1,357 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * drivers/i2c/busses/i2c-mt7621.c
+ *
+ * Copyright (C) 2013 Steven Liu <steven_liu@mediatek.com>
+ * Copyright (C) 2016 Michael Lee <igvtee@gmail.com>
+ * Copyright (C) 2018 Jan Breuer <jan.breuer@jaybee.cz>
+ *
+ * Improve driver for i2cdetect from i2c-tools to detect i2c devices on the bus.
+ * (C) 2014 Sittisak <sittisaks@hotmail.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/reset.h>
+
+#define REG_SM0CFG2_REG		0x28
+#define REG_SM0CTL0_REG		0x40
+#define REG_SM0CTL1_REG		0x44
+#define REG_SM0D0_REG		0x50
+#define REG_SM0D1_REG		0x54
+#define REG_PINTEN_REG		0x5c
+#define REG_PINTST_REG		0x60
+#define REG_PINTCL_REG		0x64
+
+/* REG_SM0CFG2_REG */
+#define SM0CFG2_IS_AUTOMODE	BIT(0)
+
+/* REG_SM0CTL0_REG */
+#define SM0CTL0_ODRAIN		BIT(31)
+#define SM0CTL0_CLK_DIV_MASK	(0x7ff << 16)
+#define SM0CTL0_CLK_DIV_MAX	0x7ff
+#define SM0CTL0_CS_STATUS       BIT(4)
+#define SM0CTL0_SCL_STATE       BIT(3)
+#define SM0CTL0_SDA_STATE       BIT(2)
+#define SM0CTL0_EN              BIT(1)
+#define SM0CTL0_SCL_STRETCH     BIT(0)
+
+/* REG_SM0CTL1_REG */
+#define SM0CTL1_ACK_MASK	(0xff << 16)
+#define SM0CTL1_PGLEN_MASK	(0x7 << 8)
+#define SM0CTL1_PGLEN(x)	((((x) - 1) << 8) & SM0CTL1_PGLEN_MASK)
+#define SM0CTL1_READ		(5 << 4)
+#define SM0CTL1_READ_LAST	(4 << 4)
+#define SM0CTL1_STOP		(3 << 4)
+#define SM0CTL1_WRITE		(2 << 4)
+#define SM0CTL1_START		(1 << 4)
+#define SM0CTL1_MODE_MASK	(0x7 << 4)
+#define SM0CTL1_TRI		BIT(0)
+
+/* timeout waiting for I2C devices to respond */
+#define TIMEOUT_MS		1000
+
+struct mtk_i2c {
+	void __iomem *base;
+	struct device *dev;
+	struct i2c_adapter adap;
+	u32 bus_freq;
+	u32 clk_div;
+	u32 flags;
+	struct clk *clk;
+};
+
+static int mtk_i2c_wait_idle(struct mtk_i2c *i2c)
+{
+	int ret;
+	u32 val;
+
+	ret = readl_relaxed_poll_timeout(i2c->base + REG_SM0CTL1_REG,
+					 val, !(val & SM0CTL1_TRI),
+					 10, TIMEOUT_MS * 1000);
+	if (ret)
+		dev_dbg(i2c->dev, "idle err(%d)\n", ret);
+
+	return ret;
+}
+
+static void mtk_i2c_reset(struct mtk_i2c *i2c)
+{
+	int ret;
+
+	ret = device_reset(i2c->adap.dev.parent);
+	if (ret)
+		dev_err(i2c->dev, "I2C reset failed!\n");
+
+	/*
+	 * Don't set SM0CTL0_ODRAIN as its bit meaning is inverted. To
+	 * configure open-drain mode, this bit needs to be cleared.
+	 */
+	iowrite32(((i2c->clk_div << 16) & SM0CTL0_CLK_DIV_MASK) | SM0CTL0_EN |
+		  SM0CTL0_SCL_STRETCH, i2c->base + REG_SM0CTL0_REG);
+	iowrite32(0, i2c->base + REG_SM0CFG2_REG);
+}
+
+static void mtk_i2c_dump_reg(struct mtk_i2c *i2c)
+{
+	dev_dbg(i2c->dev,
+		"SM0CFG2 %08x, SM0CTL0 %08x, SM0CTL1 %08x, SM0D0 %08x, SM0D1 %08x\n",
+		ioread32(i2c->base + REG_SM0CFG2_REG),
+		ioread32(i2c->base + REG_SM0CTL0_REG),
+		ioread32(i2c->base + REG_SM0CTL1_REG),
+		ioread32(i2c->base + REG_SM0D0_REG),
+		ioread32(i2c->base + REG_SM0D1_REG));
+}
+
+static int mtk_i2c_check_ack(struct mtk_i2c *i2c, u32 expected)
+{
+	u32 ack = readl_relaxed(i2c->base + REG_SM0CTL1_REG);
+	u32 ack_expected = (expected << 16) & SM0CTL1_ACK_MASK;
+
+	return ((ack & ack_expected) == ack_expected) ? 0 : -ENXIO;
+}
+
+static int mtk_i2c_master_start(struct mtk_i2c *i2c)
+{
+	iowrite32(SM0CTL1_START | SM0CTL1_TRI, i2c->base + REG_SM0CTL1_REG);
+	return mtk_i2c_wait_idle(i2c);
+}
+
+static int mtk_i2c_master_stop(struct mtk_i2c *i2c)
+{
+	iowrite32(SM0CTL1_STOP | SM0CTL1_TRI, i2c->base + REG_SM0CTL1_REG);
+	return mtk_i2c_wait_idle(i2c);
+}
+
+static int mtk_i2c_master_cmd(struct mtk_i2c *i2c, u32 cmd, int page_len)
+{
+	iowrite32(cmd | SM0CTL1_TRI | SM0CTL1_PGLEN(page_len),
+		  i2c->base + REG_SM0CTL1_REG);
+	return mtk_i2c_wait_idle(i2c);
+}
+
+static int mtk_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
+			       int num)
+{
+	struct mtk_i2c *i2c;
+	struct i2c_msg *pmsg;
+	u16 addr;
+	int i, j, ret, len, page_len;
+	u32 cmd;
+	u32 data[2];
+
+	i2c = i2c_get_adapdata(adap);
+
+	for (i = 0; i < num; i++) {
+		pmsg = &msgs[i];
+
+		/* wait hardware idle */
+		ret = mtk_i2c_wait_idle(i2c);
+		if (ret)
+			goto err_timeout;
+
+		/* start sequence */
+		ret = mtk_i2c_master_start(i2c);
+		if (ret)
+			goto err_timeout;
+
+		/* write address */
+		if (pmsg->flags & I2C_M_TEN) {
+			/* 10 bits address */
+			addr = 0xf0 | ((pmsg->addr >> 7) & 0x06);
+			addr |= (pmsg->addr & 0xff) << 8;
+			if (pmsg->flags & I2C_M_RD)
+				addr |= 1;
+			iowrite32(addr, i2c->base + REG_SM0D0_REG);
+			ret = mtk_i2c_master_cmd(i2c, SM0CTL1_WRITE, 2);
+			if (ret)
+				goto err_timeout;
+		} else {
+			/* 7 bits address */
+			addr = i2c_8bit_addr_from_msg(pmsg);
+			iowrite32(addr, i2c->base + REG_SM0D0_REG);
+			ret = mtk_i2c_master_cmd(i2c, SM0CTL1_WRITE, 1);
+			if (ret)
+				goto err_timeout;
+		}
+
+		/* check address ACK */
+		if (!(pmsg->flags & I2C_M_IGNORE_NAK)) {
+			ret = mtk_i2c_check_ack(i2c, BIT(0));
+			if (ret)
+				goto err_ack;
+		}
+
+		/* transfer data */
+		for (len = pmsg->len, j = 0; len > 0; len -= 8, j += 8) {
+			page_len = (len >= 8) ? 8 : len;
+
+			if (pmsg->flags & I2C_M_RD) {
+				cmd = (len > 8) ?
+					SM0CTL1_READ : SM0CTL1_READ_LAST;
+			} else {
+				memcpy(data, &pmsg->buf[j], page_len);
+				iowrite32(data[0], i2c->base + REG_SM0D0_REG);
+				iowrite32(data[1], i2c->base + REG_SM0D1_REG);
+				cmd = SM0CTL1_WRITE;
+			}
+
+			ret = mtk_i2c_master_cmd(i2c, cmd, page_len);
+			if (ret)
+				goto err_timeout;
+
+			if (pmsg->flags & I2C_M_RD) {
+				data[0] = ioread32(i2c->base + REG_SM0D0_REG);
+				data[1] = ioread32(i2c->base + REG_SM0D1_REG);
+				memcpy(&pmsg->buf[j], data, page_len);
+			} else {
+				if (!(pmsg->flags & I2C_M_IGNORE_NAK)) {
+					ret = mtk_i2c_check_ack(i2c,
+								(1 << page_len)
+								- 1);
+					if (ret)
+						goto err_ack;
+				}
+			}
+		}
+	}
+
+	ret = mtk_i2c_master_stop(i2c);
+	if (ret)
+		goto err_timeout;
+
+	/* the return value is number of executed messages */
+	return i;
+
+err_ack:
+	ret = mtk_i2c_master_stop(i2c);
+	if (ret)
+		goto err_timeout;
+	return -ENXIO;
+
+err_timeout:
+	mtk_i2c_dump_reg(i2c);
+	mtk_i2c_reset(i2c);
+	return ret;
+}
+
+static u32 mtk_i2c_func(struct i2c_adapter *a)
+{
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING;
+}
+
+static const struct i2c_algorithm mtk_i2c_algo = {
+	.master_xfer	= mtk_i2c_master_xfer,
+	.functionality	= mtk_i2c_func,
+};
+
+static const struct of_device_id i2c_mtk_dt_ids[] = {
+	{ .compatible = "mediatek,mt7621-i2c" },
+	{ /* sentinel */ }
+};
+
+MODULE_DEVICE_TABLE(of, i2c_mtk_dt_ids);
+
+static void mtk_i2c_init(struct mtk_i2c *i2c)
+{
+	i2c->clk_div = clk_get_rate(i2c->clk) / i2c->bus_freq - 1;
+	if (i2c->clk_div < 99)
+		i2c->clk_div = 99;
+	if (i2c->clk_div > SM0CTL0_CLK_DIV_MAX)
+		i2c->clk_div = SM0CTL0_CLK_DIV_MAX;
+
+	mtk_i2c_reset(i2c);
+}
+
+static int mtk_i2c_probe(struct platform_device *pdev)
+{
+	struct resource *res;
+	struct mtk_i2c *i2c;
+	struct i2c_adapter *adap;
+	int ret;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+
+	i2c = devm_kzalloc(&pdev->dev, sizeof(struct mtk_i2c), GFP_KERNEL);
+	if (!i2c)
+		return -ENOMEM;
+
+	i2c->base = devm_ioremap_resource(&pdev->dev, res);
+	if (IS_ERR(i2c->base))
+		return PTR_ERR(i2c->base);
+
+	i2c->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(i2c->clk)) {
+		dev_err(&pdev->dev, "no clock defined\n");
+		return PTR_ERR(i2c->clk);
+	}
+	ret = clk_prepare_enable(i2c->clk);
+	if (ret) {
+		dev_err(&pdev->dev, "Unable to enable clock\n");
+		return ret;
+	}
+
+	i2c->dev = &pdev->dev;
+
+	if (of_property_read_u32(pdev->dev.of_node, "clock-frequency",
+				 &i2c->bus_freq))
+		i2c->bus_freq = 100000;
+
+	if (i2c->bus_freq == 0) {
+		dev_warn(i2c->dev, "clock-frequency 0 not supported\n");
+		return -EINVAL;
+	}
+
+	adap = &i2c->adap;
+	adap->owner = THIS_MODULE;
+	adap->algo = &mtk_i2c_algo;
+	adap->retries = 3;
+	adap->dev.parent = &pdev->dev;
+	i2c_set_adapdata(adap, i2c);
+	adap->dev.of_node = pdev->dev.of_node;
+	strlcpy(adap->name, dev_name(&pdev->dev), sizeof(adap->name));
+
+	platform_set_drvdata(pdev, i2c);
+
+	mtk_i2c_init(i2c);
+
+	ret = i2c_add_adapter(adap);
+	if (ret < 0)
+		return ret;
+
+	dev_info(&pdev->dev, "clock %u kHz\n", i2c->bus_freq / 1000);
+
+	return ret;
+}
+
+static int mtk_i2c_remove(struct platform_device *pdev)
+{
+	struct mtk_i2c *i2c = platform_get_drvdata(pdev);
+
+	clk_disable_unprepare(i2c->clk);
+	i2c_del_adapter(&i2c->adap);
+
+	return 0;
+}
+
+static struct platform_driver mtk_i2c_driver = {
+	.probe		= mtk_i2c_probe,
+	.remove		= mtk_i2c_remove,
+	.driver		= {
+		.owner	= THIS_MODULE,
+		.name	= "i2c-mt7621",
+		.of_match_table = i2c_mtk_dt_ids,
+	},
+};
+
+module_platform_driver(mtk_i2c_driver);
+
+MODULE_AUTHOR("Steven Liu");
+MODULE_DESCRIPTION("MT7621 I2C host driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:MT7621-I2C");