diff mbox series

[v6,3/4] i2c: ch341: add I2C MFD cell driver for the CH341

Message ID 20220616013747.126051-4-frank@zago.net
State New
Headers show
Series add driver for the WCH CH341 in I2C/GPIO mode | expand

Commit Message

Frank Zago June 16, 2022, 1:37 a.m. UTC 
The I2C interface can run at 4 different speeds. This driver currently
only offer 100kHz. Tested with a variety of I2C sensors, and the IIO
subsystem.

Signed-off-by: frank zago <frank@zago.net>
---
 MAINTAINERS                    |   1 +
 drivers/i2c/busses/Kconfig     |  10 +
 drivers/i2c/busses/Makefile    |   1 +
 drivers/i2c/busses/i2c-ch341.c | 377 +++++++++++++++++++++++++++++++++
 4 files changed, 389 insertions(+)
 create mode 100644 drivers/i2c/busses/i2c-ch341.c

Comments

Randy Dunlap June 16, 2022, 5:09 a.m. UTC | #1 
Hi--

On 6/15/22 18:37, frank zago wrote:
> The I2C interface can run at 4 different speeds. This driver currently
> only offer 100kHz. Tested with a variety of I2C sensors, and the IIO
> subsystem.
> 
> Signed-off-by: frank zago <frank@zago.net>
> ---
>  MAINTAINERS                    |   1 +
>  drivers/i2c/busses/Kconfig     |  10 +
>  drivers/i2c/busses/Makefile    |   1 +
>  drivers/i2c/busses/i2c-ch341.c | 377 +++++++++++++++++++++++++++++++++
>  4 files changed, 389 insertions(+)
>  create mode 100644 drivers/i2c/busses/i2c-ch341.c
> 

> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index a1bae59208e3..db9797345ad5 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -1199,6 +1199,16 @@ config I2C_RCAR
>  
>  comment "External I2C/SMBus adapter drivers"
>  
> +config I2C_CH341
> +	tristate "CH341 USB to I2C support"
> +	select 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.

I haven't tested it, but just from reading, it looks like
this one needs a "depends on USB" since it selects MFD_CH341, which
depends on USB, and since 'select' ignores dependency chains.

The GPIO driver (patch 2/4) already depends on USB.
kernel test robot June 16, 2022, 9:18 a.m. UTC | #2 
Hi frank,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on lee-mfd/for-mfd-next]
[also build test ERROR on brgl/gpio/for-next wsa/i2c/for-next linus/master v5.19-rc2 next-20220615]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/frank-zago/add-driver-for-the-WCH-CH341-in-I2C-GPIO-mode/20220616-094113
base:   https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git for-mfd-next
config: nios2-randconfig-r026-20220616 (https://download.01.org/0day-ci/archive/20220616/202206161751.5icAiwNf-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 11.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/46c68aee86d34ee630272146a73ad7c3147bb094
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review frank-zago/add-driver-for-the-WCH-CH341-in-I2C-GPIO-mode/20220616-094113
        git checkout 46c68aee86d34ee630272146a73ad7c3147bb094
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=nios2 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   nios2-linux-ld: drivers/mfd/ch341-core.o: in function `ch341_usb_probe':
>> drivers/mfd/ch341-core.c:46: undefined reference to `usb_find_common_endpoints'
   drivers/mfd/ch341-core.c:46:(.text+0x8c): relocation truncated to fit: R_NIOS2_CALL26 against `usb_find_common_endpoints'
   nios2-linux-ld: drivers/mfd/ch341-core.o: in function `ch341_usb_driver_init':
>> drivers/mfd/ch341-core.c:86: undefined reference to `usb_register_driver'
   drivers/mfd/ch341-core.c:86:(.init.text+0x1c): relocation truncated to fit: R_NIOS2_CALL26 against `usb_register_driver'
   nios2-linux-ld: drivers/i2c/busses/i2c-ch341.o: in function `no_data_xfer':
>> drivers/i2c/busses/i2c-ch341.c:81: undefined reference to `usb_bulk_msg'
   drivers/i2c/busses/i2c-ch341.c:81:(.text+0xe0): relocation truncated to fit: R_NIOS2_CALL26 against `usb_bulk_msg'
>> nios2-linux-ld: drivers/i2c/busses/i2c-ch341.c:89: undefined reference to `usb_bulk_msg'
   drivers/i2c/busses/i2c-ch341.c:89:(.text+0x134): relocation truncated to fit: R_NIOS2_CALL26 against `usb_bulk_msg'
   nios2-linux-ld: drivers/i2c/busses/i2c-ch341.o: in function `ch341_i2c_xfer':
   drivers/i2c/busses/i2c-ch341.c:278: undefined reference to `usb_bulk_msg'
   drivers/i2c/busses/i2c-ch341.c:278:(.text+0x4e0): relocation truncated to fit: R_NIOS2_CALL26 against `usb_bulk_msg'
   nios2-linux-ld: drivers/i2c/busses/i2c-ch341.c:290: undefined reference to `usb_bulk_msg'
   drivers/i2c/busses/i2c-ch341.c:290:(.text+0x558): relocation truncated to fit: R_NIOS2_CALL26 against `usb_bulk_msg'
   nios2-linux-ld: drivers/i2c/busses/i2c-ch341.o: in function `ch341_i2c_probe':
   drivers/i2c/busses/i2c-ch341.c:357: undefined reference to `usb_bulk_msg'
   drivers/i2c/busses/i2c-ch341.c:357:(.text+0x778): relocation truncated to fit: R_NIOS2_CALL26 against `usb_bulk_msg'
   pahole: .tmp_vmlinux.btf: No such file or directory
   .btf.vmlinux.bin.o: file not recognized: file format not recognized

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for MFD_CH341
   Depends on HAS_IOMEM && USB
   Selected by
   - I2C_CH341 && I2C && HAS_IOMEM


vim +46 drivers/mfd/ch341-core.c

f33ee28d4d85a8 frank zago 2022-06-15  29  
f33ee28d4d85a8 frank zago 2022-06-15  30  static int ch341_usb_probe(struct usb_interface *iface,
f33ee28d4d85a8 frank zago 2022-06-15  31  			   const struct usb_device_id *usb_id)
f33ee28d4d85a8 frank zago 2022-06-15  32  {
f33ee28d4d85a8 frank zago 2022-06-15  33  	struct usb_endpoint_descriptor *bulk_out;
f33ee28d4d85a8 frank zago 2022-06-15  34  	struct usb_endpoint_descriptor *bulk_in;
f33ee28d4d85a8 frank zago 2022-06-15  35  	struct usb_endpoint_descriptor *intr_in;
f33ee28d4d85a8 frank zago 2022-06-15  36  	struct ch341_ddata *ddata;
f33ee28d4d85a8 frank zago 2022-06-15  37  	int ret;
f33ee28d4d85a8 frank zago 2022-06-15  38  
f33ee28d4d85a8 frank zago 2022-06-15  39  	ddata = devm_kzalloc(&iface->dev, sizeof(*ddata), GFP_KERNEL);
f33ee28d4d85a8 frank zago 2022-06-15  40  	if (!ddata)
f33ee28d4d85a8 frank zago 2022-06-15  41  		return -ENOMEM;
f33ee28d4d85a8 frank zago 2022-06-15  42  
f33ee28d4d85a8 frank zago 2022-06-15  43  	ddata->usb_dev = interface_to_usbdev(iface);
f33ee28d4d85a8 frank zago 2022-06-15  44  	mutex_init(&ddata->usb_lock);
f33ee28d4d85a8 frank zago 2022-06-15  45  
f33ee28d4d85a8 frank zago 2022-06-15 @46  	ret = usb_find_common_endpoints(iface->cur_altsetting, &bulk_in,
f33ee28d4d85a8 frank zago 2022-06-15  47  					&bulk_out, &intr_in, NULL);
f33ee28d4d85a8 frank zago 2022-06-15  48  	if (ret) {
f33ee28d4d85a8 frank zago 2022-06-15  49  		dev_err(&iface->dev, "Could not find all endpoints\n");
f33ee28d4d85a8 frank zago 2022-06-15  50  		return -ENODEV;
f33ee28d4d85a8 frank zago 2022-06-15  51  	}
f33ee28d4d85a8 frank zago 2022-06-15  52  
f33ee28d4d85a8 frank zago 2022-06-15  53  	ddata->ep_in = bulk_in->bEndpointAddress;
f33ee28d4d85a8 frank zago 2022-06-15  54  	ddata->ep_out = bulk_out->bEndpointAddress;
f33ee28d4d85a8 frank zago 2022-06-15  55  	ddata->ep_intr = intr_in->bEndpointAddress;
f33ee28d4d85a8 frank zago 2022-06-15  56  	ddata->ep_intr_interval = intr_in->bInterval;
f33ee28d4d85a8 frank zago 2022-06-15  57  
f33ee28d4d85a8 frank zago 2022-06-15  58  	usb_set_intfdata(iface, ddata);
f33ee28d4d85a8 frank zago 2022-06-15  59  
f33ee28d4d85a8 frank zago 2022-06-15  60  	ret = mfd_add_devices(&iface->dev, PLATFORM_DEVID_AUTO, ch341_devs,
f33ee28d4d85a8 frank zago 2022-06-15  61  			      ARRAY_SIZE(ch341_devs), NULL, 0, NULL);
f33ee28d4d85a8 frank zago 2022-06-15  62  	if (ret)
f33ee28d4d85a8 frank zago 2022-06-15  63  		return dev_err_probe(&iface->dev, ret,
f33ee28d4d85a8 frank zago 2022-06-15  64  				     "Failed to register child devices\n");
f33ee28d4d85a8 frank zago 2022-06-15  65  
f33ee28d4d85a8 frank zago 2022-06-15  66  	return 0;
f33ee28d4d85a8 frank zago 2022-06-15  67  }
f33ee28d4d85a8 frank zago 2022-06-15  68  
f33ee28d4d85a8 frank zago 2022-06-15  69  static void ch341_usb_disconnect(struct usb_interface *usb_if)
f33ee28d4d85a8 frank zago 2022-06-15  70  {
f33ee28d4d85a8 frank zago 2022-06-15  71  	mfd_remove_devices(&usb_if->dev);
f33ee28d4d85a8 frank zago 2022-06-15  72  }
f33ee28d4d85a8 frank zago 2022-06-15  73  
f33ee28d4d85a8 frank zago 2022-06-15  74  static const struct usb_device_id ch341_usb_table[] = {
f33ee28d4d85a8 frank zago 2022-06-15  75  	{ USB_DEVICE(0x1a86, 0x5512) },
f33ee28d4d85a8 frank zago 2022-06-15  76  	{ }
f33ee28d4d85a8 frank zago 2022-06-15  77  };
f33ee28d4d85a8 frank zago 2022-06-15  78  MODULE_DEVICE_TABLE(usb, ch341_usb_table);
f33ee28d4d85a8 frank zago 2022-06-15  79  
f33ee28d4d85a8 frank zago 2022-06-15  80  static struct usb_driver ch341_usb_driver = {
f33ee28d4d85a8 frank zago 2022-06-15  81  	.name       = "ch341-mfd",
f33ee28d4d85a8 frank zago 2022-06-15  82  	.id_table   = ch341_usb_table,
f33ee28d4d85a8 frank zago 2022-06-15  83  	.probe      = ch341_usb_probe,
f33ee28d4d85a8 frank zago 2022-06-15  84  	.disconnect = ch341_usb_disconnect,
f33ee28d4d85a8 frank zago 2022-06-15  85  };
f33ee28d4d85a8 frank zago 2022-06-15 @86  module_usb_driver(ch341_usb_driver);
f33ee28d4d85a8 frank zago 2022-06-15  87
kernel test robot June 16, 2022, 11:10 a.m. UTC | #3 
Hi frank,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on lee-mfd/for-mfd-next]
[also build test ERROR on brgl/gpio/for-next wsa/i2c/for-next linus/master v5.19-rc2 next-20220616]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/frank-zago/add-driver-for-the-WCH-CH341-in-I2C-GPIO-mode/20220616-094113
base:   https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git for-mfd-next
config: arc-buildonly-randconfig-r004-20220616 (https://download.01.org/0day-ci/archive/20220616/202206161938.BiOHSAOi-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 11.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/46c68aee86d34ee630272146a73ad7c3147bb094
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review frank-zago/add-driver-for-the-WCH-CH341-in-I2C-GPIO-mode/20220616-094113
        git checkout 46c68aee86d34ee630272146a73ad7c3147bb094
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=arc SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: "usb_bulk_msg" [drivers/i2c/busses/i2c-ch341.ko] undefined!
>> ERROR: modpost: "usb_deregister" [drivers/mfd/ch341-core.ko] undefined!
>> ERROR: modpost: "usb_register_driver" [drivers/mfd/ch341-core.ko] undefined!
>> ERROR: modpost: "usb_find_common_endpoints" [drivers/mfd/ch341-core.ko] undefined!

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for MFD_CH341
   Depends on HAS_IOMEM && USB
   Selected by
   - I2C_CH341 && I2C && HAS_IOMEM
diff mbox series

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 8b93f6192704..837065fd3150 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21480,6 +21480,7 @@  M:	Frank Zago <frank@zago.net>
 L:	linux-usb@vger.kernel.org
 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 a1bae59208e3..db9797345ad5 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -1199,6 +1199,16 @@  config I2C_RCAR
 
 comment "External I2C/SMBus adapter drivers"
 
+config I2C_CH341
+	tristate "CH341 USB to I2C support"
+	select 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 479f60e4ee3d..e83ca4a472f2 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -127,6 +127,7 @@  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..60c587cca4eb
--- /dev/null
+++ b/drivers/i2c/busses/i2c-ch341.c
@@ -0,0 +1,377 @@ 
+// 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@Harbaum.org)
+ */
+
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/mfd/ch341.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+#include <linux/usb.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
+
+/* I2C chip commands */
+#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, which includes the
+ * CH341 commands and the I2C data.
+ */
+#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];
+};
+
+/*
+ * Special case the no data transfer (SMBUS quick message), since some
+ * parameters are a bit different than the normal case.
+ */
+static int no_data_xfer(struct i2c_adapter *adapter, const struct i2c_msg *msg)
+{
+	struct ch341_i2c *dev = i2c_get_adapdata(adapter);
+	struct ch341_ddata *ddata = adapter->algo_data;
+	u8 *out = dev->i2c_buf;
+	int actual;
+	int ret;
+
+	out[0] = CH341_CMD_I2C_STREAM;
+	out[1] = CH341_CMD_I2C_STM_STA;
+	out[2] = CH341_CMD_I2C_STM_OUT;
+	out[3] = msg->addr << 1 | (msg->flags & I2C_M_RD);
+	out[4] = CH341_CMD_I2C_STM_IN;
+	out[5] = CH341_CMD_I2C_STM_STO;
+	out[6] = CH341_CMD_I2C_STM_END;
+
+	mutex_lock(&ddata->usb_lock);
+
+	/* Issue the request */
+	ret = usb_bulk_msg(ddata->usb_dev,
+			   usb_sndbulkpipe(ddata->usb_dev, ddata->ep_out),
+			   dev->i2c_buf, 7, &actual, DEFAULT_TIMEOUT_MS);
+	if (ret < 0) {
+		mutex_unlock(&ddata->usb_lock);
+		return ret;
+	}
+
+	ret = usb_bulk_msg(ddata->usb_dev,
+			   usb_rcvbulkpipe(ddata->usb_dev, ddata->ep_in),
+			   dev->i2c_buf, 2, &actual,
+			   DEFAULT_TIMEOUT_MS);
+	if (ret < 0) {
+		mutex_unlock(&ddata->usb_lock);
+		return ret;
+	}
+
+	mutex_unlock(&ddata->usb_lock);
+
+	if (actual != 2 || dev->i2c_buf[0] & 0x80)
+		return -ETIMEDOUT;
+
+	return 1;
+}
+
+/*
+ * 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_ddata *ddata = adapter->algo_data;
+	u8 *out = dev->i2c_buf;
+	int actual;
+	int ret;
+	int i;
+
+	/* Special case */
+	if (num == 1 && msgs[0].len == 0)
+		return no_data_xfer(adapter, &msgs[0]);
+
+	/* Prepare the request */
+	dev->idx_out = 0;
+	dev->out_seg = 0;
+
+	for (i = 0; i != num; i++) {
+		if (msgs[i].flags & I2C_M_RD)
+			ret = append_read(dev, &msgs[i]);
+		else
+			ret = append_write(dev, &msgs[i]);
+
+		if (ret)
+			return ret;
+	}
+
+	/* 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;
+
+	mutex_lock(&ddata->usb_lock);
+
+	/* Issue the request */
+	ret = usb_bulk_msg(ddata->usb_dev,
+			   usb_sndbulkpipe(ddata->usb_dev, ddata->ep_out),
+			   dev->i2c_buf, dev->idx_out, &actual, DEFAULT_TIMEOUT_MS);
+	if (ret < 0) {
+		mutex_unlock(&ddata->usb_lock);
+		return ret;
+	}
+
+	for (i = 0; i != num; i++) {
+		if (!(msgs[i].flags & I2C_M_RD))
+			continue;
+
+		ret = usb_bulk_msg(ddata->usb_dev,
+				  usb_rcvbulkpipe(ddata->usb_dev, ddata->ep_in),
+				  dev->i2c_buf, msgs[i].len, &actual,
+				  DEFAULT_TIMEOUT_MS);
+
+		if (ret) {
+			mutex_unlock(&ddata->usb_lock);
+			return ret;
+		}
+
+		if (actual != msgs[i].len) {
+			mutex_unlock(&ddata->usb_lock);
+			return -EIO;
+		}
+
+		memcpy(msgs[i].buf, dev->i2c_buf, actual);
+	}
+
+	mutex_unlock(&ddata->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_ddata *ddata = dev_get_drvdata(pdev->dev.parent);
+	struct ch341_i2c *ch341_i2c;
+	int actual;
+	int ret;
+
+	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 = ddata;
+	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",
+		 ddata->usb_dev->bus->busnum, ddata->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(&ddata->usb_lock);
+	ret = usb_bulk_msg(ddata->usb_dev,
+			   usb_sndbulkpipe(ddata->usb_dev, ddata->ep_out),
+			   ch341_i2c->i2c_buf, 3, &actual, DEFAULT_TIMEOUT_MS);
+	mutex_unlock(&ddata->usb_lock);
+
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret, "Cannot set I2C speed\n");
+
+	return devm_i2c_add_adapter(&pdev->dev, &ch341_i2c->adapter);
+}
+
+static struct platform_driver ch341_i2c_driver = {
+	.driver.name	= "ch341-i2c",
+	.probe		= ch341_i2c_probe,
+};
+module_platform_driver(ch341_i2c_driver);
+
+MODULE_AUTHOR("Frank Zago <frank@zago.net>");
+MODULE_DESCRIPTION("CH341 USB to I2C");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ch341-i2c");