Index: arch/amd64/amd64/conf.c
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/conf.c,v
retrieving revision 1.71
diff -u -p -r1.71 conf.c
--- arch/amd64/amd64/conf.c	6 Jul 2020 04:32:25 -0000	1.71
+++ arch/amd64/amd64/conf.c	14 Sep 2020 23:55:07 -0000
@@ -158,6 +158,8 @@ cdev_decl(nvram);
 cdev_decl(drm);
 #include "viocon.h"
 cdev_decl(viocon);
+#include "iic.h"
+cdev_decl(iic);
 
 #include "wsdisplay.h"
 #include "wskbd.h"
@@ -295,6 +297,7 @@ struct cdevsw	cdevsw[] =
 	cdev_switch_init(NSWITCH,switch), /* 97: switch(4) control interface */
 	cdev_fido_init(NFIDO,fido),	/* 98: FIDO/U2F security keys */
 	cdev_pppx_init(NPPPX,pppac),	/* 99: PPP Access Concentrator */
+	cdev_iic_init(NIIC,iic),	/* 100: I2C (iic) access */
 };
 int	nchrdev = nitems(cdevsw);
 
Index: dev/i2c/files.i2c
===================================================================
RCS file: /cvs/src/sys/dev/i2c/files.i2c,v
retrieving revision 1.66
diff -u -p -r1.66 files.i2c
--- dev/i2c/files.i2c	18 Jun 2020 18:05:00 -0000	1.66
+++ dev/i2c/files.i2c	14 Sep 2020 23:55:08 -0000
@@ -4,7 +4,7 @@
 define	i2c {[addr = -1], [size = -1]}
 device	iic: i2c
 attach	iic at i2cbus
-file	dev/i2c/i2c.c				iic | i2cbus
+file	dev/i2c/i2c.c				iic | i2cbus needs-flag
 file	dev/i2c/i2c_exec.c			iic | i2cbus
 file	dev/i2c/i2c_scan.c			iic | i2cbus
 
Index: dev/i2c/i2c.c
===================================================================
RCS file: /cvs/src/sys/dev/i2c/i2c.c,v
retrieving revision 1.16
diff -u -p -r1.16 i2c.c
--- dev/i2c/i2c.c	14 Mar 2015 03:38:47 -0000	1.16
+++ dev/i2c/i2c.c	14 Sep 2020 23:55:08 -0000
@@ -143,3 +143,109 @@ iic_attach(struct device *parent, struct
 	else
 		iic_scan(self, aux);
 }
+
+static struct iic_softc *
+iic_lookup(dev_t dev)
+{
+	unsigned int unit = minor(dev);
+	unsigned int master = IIC_MASTER(unit);
+
+	if (master > iic_cd.cd_ndevs)
+		return (NULL);
+
+	return (iic_cd.cd_devs[master]);
+}
+
+int
+iicopen(dev_t dev, int flags, int mode, struct proc *p)
+{
+	struct iic_softc *sc;
+	unsigned int unit = minor(dev);
+
+	sc = iic_lookup(dev);
+	if (sc == NULL)
+		return (ENXIO);
+
+	if (IIC_ADDR_TYPE(unit) != IIC_ADDR_TYPE_7B) {
+		/* XXX */
+		return (ENXIO);
+	}
+
+	return (0);
+}
+
+static int
+iic_ioc_exec(struct iic_softc *sc, i2c_addr_t addr, struct iic_ioc_op *iio)
+{
+	uint8_t cmd[IIC_CMD_MAXLEN];
+	uint8_t buf[IIC_CMD_MAXLEN];
+	int error;
+
+	if (iio->iio_cmdlen > sizeof(cmd))
+		return (ENOBUFS); /* wat */
+	if (iio->iio_buflen > sizeof(buf))
+		return (ENOBUFS);
+
+	if (iio->iio_cmdlen > 0) {
+		error = copyin(iio->iio_cmd, cmd, iio->iio_cmdlen);
+		if (error != 0)
+			return (error);
+	}
+
+	if (iio->iio_buflen > 0 && I2C_OP_WRITE_P(iio->iio_op)) {
+		error = copyin(iio->iio_buf, buf, iio->iio_buflen);
+		if (error != 0)
+			return (error);
+	}
+
+	error = iic_acquire_bus(sc->sc_tag, 0);
+	if (error != 0)
+		return (error);
+
+	if (iic_exec(sc->sc_tag, iio->iio_op, addr,
+	    cmd, iio->iio_cmdlen, buf, iio->iio_buflen, 0) != 0)
+		error = EIO;
+
+	iic_release_bus(sc->sc_tag, 0);
+
+	if (error != 0)
+		return (error);
+
+	if (iio->iio_buflen > 0 && I2C_OP_READ_P(iio->iio_op)) {
+		error = copyout(buf, iio->iio_buf, iio->iio_buflen);
+		if (error != 0)
+			return (error);
+	}
+
+	return (0);
+}
+
+int
+iicioctl(dev_t dev, u_long cmd, caddr_t addr, int flags, struct proc *p)
+{
+	struct iic_softc *sc;
+	unsigned int unit = minor(dev);
+	int error = 0;
+
+	sc = iic_lookup(dev);
+	if (sc == NULL)
+		return (ENXIO);
+
+	switch (cmd) {
+	case I2C_IOCTL_EXEC:
+		error = iic_ioc_exec(sc, IIC_ADDR(unit),
+		    (struct iic_ioc_op *)addr);
+		break;
+	default:
+		error = ENOTTY;
+		break;
+	}
+
+	return (error);
+}
+
+int
+iicclose(dev_t dev, int flags, int mode, struct proc *p)
+{
+	return (0);
+}
Index: dev/i2c/i2c_io.h
===================================================================
RCS file: /cvs/src/sys/dev/i2c/i2c_io.h,v
retrieving revision 1.2
diff -u -p -r1.2 i2c_io.h
--- dev/i2c/i2c_io.h	11 Jan 2020 11:30:47 -0000	1.2
+++ dev/i2c/i2c_io.h	14 Sep 2020 23:55:08 -0000
@@ -86,24 +86,40 @@ typedef enum {
  * I2C_OP_WRITE and I2C_OP_READ.
  */
 
-#ifdef notyet
 /*
- * I2C_IOCTL_EXEC:
- *
- *	User ioctl to execute an i2c operation.
+ * The iic(4) dev_t minor is split into parts that identify the
+ * master (ie, which iic(4) device) and a slave attached to that
+ * master. The slave portion is big enough to hold a 10 bit address,
+ * plus a flag that identifies if it is a 10bit address or not.
  */
-typedef struct i2c_ioctl_exec {
-	i2c_op_t iie_op;		/* operation to perform */
-	i2c_addr_t iie_addr;		/* address of device */
-	const void *iie_cmd;		/* pointer to command */
-	size_t iie_cmdlen;		/* length of command */
-	void *iie_buf;			/* pointer to data buffer */
-	size_t iie_buflen;		/* length of data buffer */
-} i2c_ioctl_exec_t;
-#define	I2C_EXEC_MAX_CMDLEN	32
-#define	I2C_EXEC_MAX_BUFLEN	32
 
-#define	I2C_IOCTL_EXEC		 _IOW('I', 0, i2c_ioctl_exec_t)
-#endif
+#define IIC_SLAVE_BITS		12
+
+#define IIC_MASTER(_u)		((_u) >> IIC_SLAVE_BITS)
+#define IIC_SLAVE(_u)		((_u) & ((1 << IIC_SLAVE_BITS) - 1))
+
+#define IIC_ADDR_BITS		10
+#define IIC_ADDR_MASK		((1 << IIC_ADDR_BITS) - 1)
+#define IIC_ADDR(_u)		((_u) & IIC_ADDR_MASK)
+
+#define IIC_ADDR_TYPE_SHIFT	(IIC_ADDR_BITS + 1)
+#define IIC_ADDR_TYPE_MASK	(1U << IIC_ADDR_TYPE_SHIFT)
+#define IIC_ADDR_TYPE(_a)	((_a) & IIC_ADDR_TYPE_MASK)
+#define IIC_ADDR_TYPE_7B	(0U << IIC_ADDR_TYPE_SHIFT)
+#define IIC_ADDR_TYPE_10B	(1U << IIC_ADDR_TYPE_SHIFT)
+
+#define	IIC_CMD_MAXLEN		32
+#define	IIC_BUF_MAXLEN		32
+
+struct iic_ioc_op {
+	i2c_op_t	 iio_op;
+	i2c_addr_t	 iio_addr;
+	const void 	*iio_cmd;
+	size_t		 iio_cmdlen;
+	void		*iio_buf;
+	size_t		 iio_buflen;
+};
+
+#define	I2C_IOCTL_EXEC		 _IOW('2', 0, struct iic_ioc_op)
 
 #endif /* _DEV_I2C_I2C_IO_H_ */
Index: sys/conf.h
===================================================================
RCS file: /cvs/src/sys/sys/conf.h,v
retrieving revision 1.155
diff -u -p -r1.155 conf.h
--- sys/conf.h	6 Jul 2020 04:11:26 -0000	1.155
+++ sys/conf.h	14 Sep 2020 23:55:09 -0000
@@ -300,6 +300,13 @@ extern struct cdevsw cdevsw[];
 	(dev_type_stop((*))) enodev, 0, selfalse, \
 	(dev_type_mmap((*))) enodev }
 
+/* open, close, ioctl */
+#define       cdev_iic_init(c,n) { \
+	dev_init(c,n,open), dev_init(c,n,close), (dev_type_read((*))) enodev, \
+	(dev_type_write((*))) enodev, dev_init(c,n,ioctl), \
+	(dev_type_stop((*))) enodev, 0, selfalse, \
+	(dev_type_mmap((*))) enodev }
+
 /* open, close, ioctl, mmap */
 #define	cdev_fb_init(c,n) { \
 	dev_init(c,n,open), dev_init(c,n,close), (dev_type_read((*))) enodev, \