[PATCH v4 3/3] i2c: ch341: add MFD cell driver CH341 for I2C

[frank zago <frank@xxxxxxxx>]

The I2C interface can run at 4 different speeds. This driver currently
only offer 100MHz. Tested with a variety of I2C sensors, and the IIO
subsystem.

Signed-off-by: frank zago <frank@xxxxxxxx>
---
 MAINTAINERS                    |   1 +
 drivers/i2c/busses/Kconfig     |  10 +
 drivers/i2c/busses/Makefile    |   1 +
 drivers/i2c/busses/i2c-ch341.c | 325 +++++++++++++++++++++++++++++++++
 drivers/mfd/ch341-core.c       |   3 +
 5 files changed, 340 insertions(+)
 create mode 100644 drivers/i2c/busses/i2c-ch341.c

diff --git a/MAINTAINERS b/MAINTAINERS
index fdff76a5d9b0..ba367013b463 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20850,6 +20850,7 @@ M:	Frank Zago <frank@xxxxxxxx>
 L:	linux-usb@xxxxxxxxxxxxxxx
 S:	Maintained
 F:	drivers/gpio/gpio-ch341.c
+F:	drivers/i2c/busses/i2c-ch341.c
 F:	drivers/mfd/ch341-core.c
 F:	include/linux/mfd/ch341.h
 
diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 8a6c6ee28556..987645220d20 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -1178,6 +1178,16 @@ config I2C_RCAR
 
 comment "External I2C/SMBus adapter drivers"
 
+config I2C_CH341
+	tristate "CH341 USB adapter in GPIO/I2C/SPI mode"
+	depends on MFD_CH341
+	help
+	  If you say yes to this option, I2C support will be included for the
+	  WCH CH341, a USB to I2C/SPI/GPIO interface.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called i2c-ch341.
+
 config I2C_DIOLAN_U2C
 	tristate "Diolan U2C-12 USB adapter"
 	depends on USB
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index 1d00dce77098..bca529c325b8 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -123,6 +123,7 @@ obj-$(CONFIG_I2C_XLP9XX)	+= i2c-xlp9xx.o
 obj-$(CONFIG_I2C_RCAR)		+= i2c-rcar.o
 
 # External I2C/SMBus adapter drivers
+obj-$(CONFIG_I2C_CH341)		+= i2c-ch341.o
 obj-$(CONFIG_I2C_DIOLAN_U2C)	+= i2c-diolan-u2c.o
 obj-$(CONFIG_I2C_DLN2)		+= i2c-dln2.o
 obj-$(CONFIG_I2C_CP2615) += i2c-cp2615.o
diff --git a/drivers/i2c/busses/i2c-ch341.c b/drivers/i2c/busses/i2c-ch341.c
new file mode 100644
index 000000000000..f1fbc6e349fa
--- /dev/null
+++ b/drivers/i2c/busses/i2c-ch341.c
@@ -0,0 +1,325 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * I2C cell driver for the CH341A, CH341B and CH341T.
+ *
+ * Copyright 2022, Frank Zago
+ * Copyright (c) 2016 Tse Lun Bien
+ * Copyright (c) 2014 Marco Gittler
+ * Copyright (C) 2006-2007 Till Harbaum (Till@xxxxxxxxxxx)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/platform_device.h>
+
+#include <linux/mfd/ch341.h>
+
+/* I2C bus speed. Speed selection is not implemented. */
+#define CH341_I2C_20KHZ  0
+#define CH341_I2C_100KHZ 1
+#define CH341_I2C_400KHZ 2
+#define CH341_I2C_750KHZ 3
+
+#define CH341_CMD_I2C_STREAM 0xAA
+#define CH341_CMD_I2C_STM_END 0x00
+
+#define CH341_CMD_I2C_STM_STA 0x74
+#define CH341_CMD_I2C_STM_STO 0x75
+#define CH341_CMD_I2C_STM_OUT 0x80
+#define CH341_CMD_I2C_STM_IN 0xC0
+#define CH341_CMD_I2C_STM_SET 0x60
+
+/* The maximum request size is 4096 bytes, both for reading and
+ * writing, split in up to 128 32-byte segments. The I2C stream must
+ * start and stop in each 32-byte segment. Reading must also be split,
+ * with up to 32-byte per segment.
+ */
+#define SEG_COUNT 128
+
+/* Limit the transfer size that can be written. 4KiB is the maximum
+ * size of the whole buffer, but it must include all the command
+ * delimiters. 3KiB sounds reasonable.
+ */
+#define MAX_RW_LENGTH 3072
+
+struct ch341_i2c {
+	struct i2c_adapter adapter;
+
+	/* I2C request and response state */
+	int idx_out;		/* current offset in buf */
+	int out_seg;		/* current segment */
+	u8 i2c_buf[SEG_COUNT * SEG_SIZE];
+};
+
+/* Append a write command to the current request. A set of 32-byte
+ * packets is filled. Each packet starts with STREAM and finishes with
+ * END, and contains an OUT field, leaving up to 29 bytes of data. The
+ * first packet must also include a START and the device address.
+ */
+static int append_write(struct ch341_i2c *dev, const struct i2c_msg *msg)
+{
+	bool start_done = false;
+	u8 *out = dev->i2c_buf;
+	int len;
+	u8 *p;
+
+	len = msg->len;
+	p = msg->buf;
+
+	while (len) {
+		int to_write;
+		int avail;
+
+		if (dev->idx_out % SEG_SIZE) {
+			/* Finish current packet, and advance to the next one */
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_END;
+			dev->out_seg++;
+			dev->idx_out = dev->out_seg * SEG_SIZE;
+
+			if (dev->out_seg == SEG_COUNT)
+				return -E2BIG;
+		}
+
+		out[dev->idx_out++] = CH341_CMD_I2C_STREAM;
+
+		/* account for stream start and end */
+		avail = SEG_SIZE - 3;
+
+		if (!start_done) {
+			/* Each message has a start */
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_STA;
+
+			avail -= 2; /* room for STA and device address */
+		}
+
+		to_write = min_t(int, len, avail);
+
+		if (!start_done) {
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_OUT | (to_write + 1);
+			out[dev->idx_out++] = msg->addr << 1;
+
+			start_done = true;
+		} else {
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_OUT | to_write;
+		}
+
+		memcpy(&out[dev->idx_out], p, to_write);
+		dev->idx_out += to_write;
+		len -= to_write;
+		p += to_write;
+	}
+
+	return 0;
+}
+
+/* Append a read command to the request. It usually follows a write
+ * command. When that happens, the driver will attempt to concat the
+ * read command into the same packet.  Each read command, of up to 32
+ * bytes, must be written to a new packet. It is not possible to
+ * concat them.
+ */
+static int append_read(struct ch341_i2c *dev, const struct i2c_msg *msg)
+{
+	bool start_done = false;
+	u8 *out = dev->i2c_buf;
+	int len;
+
+	len = msg->len;
+
+	while (len) {
+		int to_read;
+
+		if (dev->idx_out % SEG_SIZE) {
+			if (!start_done &&
+			    (dev->idx_out % SEG_SIZE) <  (SEG_SIZE - 7)) {
+				/* There's enough left for a read */
+			} else {
+				/* Finish current packet, and advance to the next one */
+				out[dev->idx_out++] = CH341_CMD_I2C_STM_END;
+				dev->out_seg++;
+				dev->idx_out = dev->out_seg * SEG_SIZE;
+
+				if (dev->out_seg == SEG_COUNT)
+					return -E2BIG;
+
+				out[dev->idx_out++] = CH341_CMD_I2C_STREAM;
+			}
+		} else {
+			out[dev->idx_out++] = CH341_CMD_I2C_STREAM;
+		}
+
+		if (!start_done) {
+			/* Each message has a start */
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_STA;
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_OUT | 1;
+			out[dev->idx_out++] = msg->addr << 1 | 1;
+
+			start_done = true;
+		}
+
+		/* Apparently the last command must be an STM_IN to
+		 * read the last byte. Without it, the adapter gets
+		 * lost.
+		 */
+		to_read = min_t(int, len, 32);
+		len -= to_read;
+		if (len == 0) {
+			if (to_read > 1)
+				out[dev->idx_out++] = CH341_CMD_I2C_STM_IN | (to_read - 1);
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_IN;
+		} else {
+			out[dev->idx_out++] = CH341_CMD_I2C_STM_IN | to_read;
+		}
+	}
+
+	return 0;
+}
+
+static int ch341_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
+{
+	struct ch341_i2c *dev = i2c_get_adapdata(adapter);
+	struct ch341_device *ch341 = adapter->algo_data;
+	u8 *out = dev->i2c_buf;
+	int actual;
+	int rc;
+	int i;
+
+	/* Prepare the request */
+	dev->idx_out = 0;
+	dev->out_seg = 0;
+
+	for (i = 0; i != num; i++) {
+		if (msgs[i].flags & I2C_M_RD)
+			rc = append_read(dev, &msgs[i]);
+		else
+			rc = append_write(dev, &msgs[i]);
+
+		if (rc)
+			return rc;
+	}
+
+	/* Finish the last packet */
+	if (SEG_SIZE - (dev->idx_out % SEG_SIZE) < 2) {
+		out[dev->idx_out++] = CH341_CMD_I2C_STM_END;
+
+		dev->out_seg++;
+		if (dev->out_seg == SEG_COUNT)
+			return -E2BIG;
+
+		dev->idx_out = dev->out_seg * SEG_SIZE;
+
+		out[dev->idx_out++] = CH341_CMD_I2C_STREAM;
+	}
+
+	out[dev->idx_out++] = CH341_CMD_I2C_STM_STO;
+	out[dev->idx_out++] = CH341_CMD_I2C_STM_END;
+
+	dev_dbg(&adapter->dev, "bulk_out request with %d bytes\n",
+		dev->idx_out);
+
+	mutex_lock(&ch341->usb_lock);
+
+	/* Issue the request */
+	rc = usb_bulk_msg(ch341->usb_dev,
+			      usb_sndbulkpipe(ch341->usb_dev, ch341->ep_out),
+			      dev->i2c_buf, dev->idx_out, &actual, DEFAULT_TIMEOUT);
+	if (rc < 0) {
+		mutex_unlock(&ch341->usb_lock);
+		return rc;
+	}
+
+	for (i = 0; i != num; i++) {
+		if (!(msgs[i].flags & I2C_M_RD))
+			continue;
+
+		rc = usb_bulk_msg(ch341->usb_dev,
+				      usb_rcvbulkpipe(ch341->usb_dev, ch341->ep_in),
+				      dev->i2c_buf, msgs[i].len, &actual, DEFAULT_TIMEOUT);
+
+		if (rc) {
+			mutex_unlock(&ch341->usb_lock);
+			return rc;
+		}
+
+		if (actual != msgs[i].len) {
+			mutex_unlock(&ch341->usb_lock);
+			return -EIO;
+		}
+
+		memcpy(msgs[i].buf, dev->i2c_buf, actual);
+	}
+
+	mutex_unlock(&ch341->usb_lock);
+
+	return num;
+}
+
+static u32 ch341_i2c_func(struct i2c_adapter *adap)
+{
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
+}
+
+static const struct i2c_algorithm ch341_i2c_algorithm = {
+	.master_xfer = ch341_i2c_xfer,
+	.functionality = ch341_i2c_func,
+};
+
+static const struct i2c_adapter_quirks ch341_i2c_quirks = {
+	.max_read_len = MAX_RW_LENGTH,
+	.max_write_len = MAX_RW_LENGTH,
+};
+
+static int ch341_i2c_probe(struct platform_device *pdev)
+{
+	struct ch341_device *ch341 = dev_get_drvdata(pdev->dev.parent);
+	struct ch341_i2c *ch341_i2c;
+	int actual;
+	int rc;
+
+	ch341_i2c = devm_kzalloc(&pdev->dev, sizeof(*ch341_i2c), GFP_KERNEL);
+	if (ch341_i2c == NULL)
+		return -ENOMEM;
+
+	ch341_i2c->adapter.owner = THIS_MODULE;
+	ch341_i2c->adapter.class = I2C_CLASS_HWMON;
+	ch341_i2c->adapter.algo = &ch341_i2c_algorithm;
+	ch341_i2c->adapter.algo_data = ch341;
+	ch341_i2c->adapter.quirks = &ch341_i2c_quirks;
+	ch341_i2c->adapter.dev.parent = &pdev->dev;
+	snprintf(ch341_i2c->adapter.name, sizeof(ch341_i2c->adapter.name),
+		 "CH341 I2C USB bus %03d device %03d",
+		 ch341->usb_dev->bus->busnum, ch341->usb_dev->devnum);
+
+	i2c_set_adapdata(&ch341_i2c->adapter, ch341_i2c);
+	platform_set_drvdata(pdev, ch341_i2c);
+
+	/* Set ch341 i2c speed */
+	ch341_i2c->i2c_buf[0] = CH341_CMD_I2C_STREAM;
+	ch341_i2c->i2c_buf[1] = CH341_CMD_I2C_STM_SET | CH341_I2C_100KHZ;
+	ch341_i2c->i2c_buf[2] = CH341_CMD_I2C_STM_END;
+	mutex_lock(&ch341->usb_lock);
+	rc = usb_bulk_msg(ch341->usb_dev,
+			      usb_sndbulkpipe(ch341->usb_dev, ch341->ep_out),
+			      ch341_i2c->i2c_buf, 3, &actual, DEFAULT_TIMEOUT);
+	mutex_unlock(&ch341->usb_lock);
+	if (rc < 0) {
+		dev_err(&pdev->dev, "Cannot set I2C speed\n");
+		return rc;
+	}
+
+	return devm_i2c_add_adapter(&pdev->dev, &ch341_i2c->adapter);
+}
+
+static struct platform_driver ch341_i2c_driver = {
+	.driver.name	= "ch341-i2c",
+	.driver.owner	= THIS_MODULE,
+	.probe		= ch341_i2c_probe,
+};
+
+module_platform_driver(ch341_i2c_driver);
+
+MODULE_AUTHOR("Various");
+MODULE_DESCRIPTION("CH341 USB to I2C");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:ch341-i2c");
diff --git a/drivers/mfd/ch341-core.c b/drivers/mfd/ch341-core.c
index 85e0ae812098..400e44bd71ef 100644
--- a/drivers/mfd/ch341-core.c
+++ b/drivers/mfd/ch341-core.c
@@ -22,6 +22,9 @@ static const struct mfd_cell ch341_devs[] = {
 	{
 		.name = "ch341-gpio",
 	},
+	{
+		.name = "ch341-i2c",
+	},
 };
 
 static int ch341_usb_probe(struct usb_interface *iface,
-- 
2.32.0