i2c: improve RECV_LEN documentation & usage

index f71a1751cacf..8d2f59f53324 100644
@@ -32,18 +32,41 @@
 
 /**
  * struct i2c_msg - an I2C transaction segment beginning with START
- * @addr: Slave address, either seven or ten bits.  When this is a ten
- *	bit address, I2C_M_TEN must be set in @flags and the adapter
- *	must support I2C_FUNC_10BIT_ADDR.
- * @flags: I2C_M_RD is handled by all adapters.  No other flags may be
- *	provided unless the adapter exported the relevant I2C_FUNC_*
- *	flags through i2c_check_functionality().
- * @len: Number of data bytes in @buf being read from or written to the
- *	I2C slave address.  For read transactions where I2C_M_RECV_LEN
- *	is set, the caller guarantees that this buffer can hold up to
- *	32 bytes in addition to the initial length byte sent by the
- *	slave (plus, if used, the SMBus PEC); and this value will be
- *	incremented by the number of block data bytes received.
+ *
+ * @addr: Slave address, either 7 or 10 bits. When this is a 10 bit address,
+ *   %I2C_M_TEN must be set in @flags and the adapter must support
+ *   %I2C_FUNC_10BIT_ADDR.
+ *
+ * @flags:
+ *   Supported by all adapters:
+ *   %I2C_M_RD: read data (from slave to master). Guaranteed to be 0x0001!
+ *
+ *   Optional:
+ *   %I2C_M_DMA_SAFE: the buffer of this message is DMA safe. Makes only sense
+ *     in kernelspace, because userspace buffers are copied anyway
+ *
+ *   Only if I2C_FUNC_10BIT_ADDR is set:
+ *   %I2C_M_TEN: this is a 10 bit chip address
+ *
+ *   Only if I2C_FUNC_SMBUS_READ_BLOCK_DATA is set:
+ *   %I2C_M_RECV_LEN: message length will be first received byte
+ *
+ *   Only if I2C_FUNC_NOSTART is set:
+ *   %I2C_M_NOSTART: skip repeated start sequence
+
+ *   Only if I2C_FUNC_PROTOCOL_MANGLING is set:
+ *   %I2C_M_NO_RD_ACK: in a read message, master ACK/NACK bit is skipped
+ *   %I2C_M_IGNORE_NAK: treat NACK from client as ACK
+ *   %I2C_M_REV_DIR_ADDR: toggles the Rd/Wr bit
+ *   %I2C_M_STOP: force a STOP condition after the message
+ *
+ * @len: Number of data bytes in @buf being read from or written to the I2C
+ *   slave address. For read transactions where %I2C_M_RECV_LEN is set, the
+ *   caller guarantees that this buffer can hold up to %I2C_SMBUS_BLOCK_MAX
+ *   bytes in addition to the initial length byte sent by the slave (plus,
+ *   if used, the SMBus PEC); and this value will be incremented by the number
+ *   of block data bytes received.
+ *
  * @buf: The buffer into which data is read, or from which it's written.
  *
  * An i2c_msg is the low level representation of one segment of an I2C

@@ -60,40 +83,36 @@
  * group, it is followed by a STOP.  Otherwise it is followed by the next
  * @i2c_msg transaction segment, beginning with a (repeated) START.
  *
- * Alternatively, when the adapter supports I2C_FUNC_PROTOCOL_MANGLING then
+ * Alternatively, when the adapter supports %I2C_FUNC_PROTOCOL_MANGLING then
  * passing certain @flags may have changed those standard protocol behaviors.
  * Those flags are only for use with broken/nonconforming slaves, and with
- * adapters which are known to support the specific mangling options they
- * need (one or more of IGNORE_NAK, NO_RD_ACK, NOSTART, and REV_DIR_ADDR).
+ * adapters which are known to support the specific mangling options they need.
  */
 struct i2c_msg {
-	__u16 addr;	/* slave address			*/
+	__u16 addr;
 	__u16 flags;
-#define I2C_M_RD		0x0001	/* read data, from slave to master */
-					/* I2C_M_RD is guaranteed to be 0x0001! */
-#define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
-#define I2C_M_DMA_SAFE		0x0200	/* the buffer of this message is DMA safe */
-					/* makes only sense in kernelspace */
-					/* userspace buffers are copied anyway */
-#define I2C_M_RECV_LEN		0x0400	/* length will be first received byte */
-#define I2C_M_NO_RD_ACK		0x0800	/* if I2C_FUNC_PROTOCOL_MANGLING */
-#define I2C_M_IGNORE_NAK	0x1000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-#define I2C_M_REV_DIR_ADDR	0x2000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-#define I2C_M_NOSTART		0x4000	/* if I2C_FUNC_NOSTART */
-#define I2C_M_STOP		0x8000	/* if I2C_FUNC_PROTOCOL_MANGLING */
-	__u16 len;		/* msg length				*/
-	__u8 *buf;		/* pointer to msg data			*/
+#define I2C_M_RD		0x0001	/* guaranteed to be 0x0001! */
+#define I2C_M_TEN		0x0010	/* use only if I2C_FUNC_10BIT_ADDR */
+#define I2C_M_DMA_SAFE		0x0200	/* use only in kernel space */
+#define I2C_M_RECV_LEN		0x0400	/* use only if I2C_FUNC_SMBUS_READ_BLOCK_DATA */
+#define I2C_M_NO_RD_ACK		0x0800	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
+#define I2C_M_IGNORE_NAK	0x1000	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
+#define I2C_M_REV_DIR_ADDR	0x2000	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
+#define I2C_M_NOSTART		0x4000	/* use only if I2C_FUNC_NOSTART */
+#define I2C_M_STOP		0x8000	/* use only if I2C_FUNC_PROTOCOL_MANGLING */
+	__u16 len;
+	__u8 *buf;
 };
 
 /* To determine what functionality is present */
 
 #define I2C_FUNC_I2C			0x00000001
-#define I2C_FUNC_10BIT_ADDR		0x00000002
-#define I2C_FUNC_PROTOCOL_MANGLING	0x00000004 /* I2C_M_IGNORE_NAK etc. */
+#define I2C_FUNC_10BIT_ADDR		0x00000002 /* required for I2C_M_TEN */
+#define I2C_FUNC_PROTOCOL_MANGLING	0x00000004 /* required for I2C_M_IGNORE_NAK etc. */
 #define I2C_FUNC_SMBUS_PEC		0x00000008
-#define I2C_FUNC_NOSTART		0x00000010 /* I2C_M_NOSTART */
+#define I2C_FUNC_NOSTART		0x00000010 /* required for I2C_M_NOSTART */
 #define I2C_FUNC_SLAVE			0x00000020
-#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL	0x00008000 /* SMBus 2.0 */
+#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL	0x00008000 /* SMBus 2.0 or later */
 #define I2C_FUNC_SMBUS_QUICK		0x00010000
 #define I2C_FUNC_SMBUS_READ_BYTE	0x00020000
 #define I2C_FUNC_SMBUS_WRITE_BYTE	0x00040000

@@ -102,11 +121,11 @@ struct i2c_msg {
 #define I2C_FUNC_SMBUS_READ_WORD_DATA	0x00200000
 #define I2C_FUNC_SMBUS_WRITE_WORD_DATA	0x00400000
 #define I2C_FUNC_SMBUS_PROC_CALL	0x00800000
-#define I2C_FUNC_SMBUS_READ_BLOCK_DATA	0x01000000
+#define I2C_FUNC_SMBUS_READ_BLOCK_DATA	0x01000000 /* required for I2C_M_RECV_LEN */
 #define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000
 #define I2C_FUNC_SMBUS_READ_I2C_BLOCK	0x04000000 /* I2C-like block xfer  */
 #define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK	0x08000000 /* w/ 1-byte reg. addr. */
-#define I2C_FUNC_SMBUS_HOST_NOTIFY	0x10000000
+#define I2C_FUNC_SMBUS_HOST_NOTIFY	0x10000000 /* SMBus 2.0 or later */
 
 #define I2C_FUNC_SMBUS_BYTE		(I2C_FUNC_SMBUS_READ_BYTE | \
 					 I2C_FUNC_SMBUS_WRITE_BYTE)

index 8d2f59f53324..7786551eb177 100644
@@ -1,29 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
-/* ------------------------------------------------------------------------- */
-/*									     */
-/* i2c.h - definitions for the i2c-bus interface			     */
-/*									     */
-/* ------------------------------------------------------------------------- */
-/*   Copyright (C) 1995-2000 Simon G. Vogl
-
-    This program is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program; if not, write to the Free Software
-    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
-    MA 02110-1301 USA.							     */
-/* ------------------------------------------------------------------------- */
-
-/* With some changes from Kyösti Mälkki <[email protected]> and
-   Frodo Looijaard <[email protected]> */
+/*
+ * i2c.h - definitions for the I2C bus interface
+ *
+ * Copyright (C) 1995-2000 Simon G. Vogl
+ * With some changes from Kyösti Mälkki <[email protected]> and
+ * Frodo Looijaard <[email protected]>
+ */
 
 #ifndef _UAPI_LINUX_I2C_H
 #define _UAPI_LINUX_I2C_H

index 85f8047afcf2..1c4cec4ddd84 100644
@@ -1,25 +1,10 @@
 /* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
 /*
-    i2c-dev.h - i2c-bus driver, char device interface
-
-    Copyright (C) 1995-97 Simon G. Vogl
-    Copyright (C) 1998-99 Frodo Looijaard <[email protected]>
-
-    This program is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program; if not, write to the Free Software
-    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
-    MA 02110-1301 USA.
-*/
+ * i2c-dev.h - I2C bus char device interface
+ *
+ * Copyright (C) 1995-97 Simon G. Vogl
+ * Copyright (C) 1998-99 Frodo Looijaard <[email protected]>
+ */
 
 #ifndef _UAPI_LINUX_I2C_DEV_H
 #define _UAPI_LINUX_I2C_DEV_H

index d9607905dc2f..845eda70b8ca 100644
@@ -347,7 +347,7 @@ static int octeon_i2c_read(struct octeon_i2c *i2c, int target,
 		if (result)
 			return result;
 		if (recv_len && i == 0) {
-			if (data[i] > I2C_SMBUS_BLOCK_MAX + 1)
+			if (data[i] > I2C_SMBUS_BLOCK_MAX)
 				return -EPROTO;
 			length += data[i];
 		}

index 7786551eb177..92326ebde350 100644
@@ -129,6 +129,11 @@ struct i2c_msg {
 					 I2C_FUNC_SMBUS_I2C_BLOCK | \
 					 I2C_FUNC_SMBUS_PEC)
 
+/* if I2C_M_RECV_LEN is also supported */
+#define I2C_FUNC_SMBUS_EMUL_ALL		(I2C_FUNC_SMBUS_EMUL | \
+					 I2C_FUNC_SMBUS_READ_BLOCK_DATA | \
+					 I2C_FUNC_SMBUS_BLOCK_PROC_CALL)
+
 /*
  * Data for SMBus Messages
  */

index 913db013fe90..fc90293afcbf 100644
@@ -622,9 +622,7 @@ static int bit_xfer_atomic(struct i2c_adapter *i2c_adap, struct i2c_msg msgs[],
 
 static u32 bit_func(struct i2c_adapter *adap)
 {
-	return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL |
-	       I2C_FUNC_SMBUS_READ_BLOCK_DATA |
-	       I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
+	return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL_ALL |
 	       I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
 }
 

index 5a47915869ae..61dc20fd1191 100644
@@ -1603,7 +1603,7 @@ static int qup_i2c_xfer_v2(struct i2c_adapter *adap,
 
 static u32 qup_i2c_func(struct i2c_adapter *adap)
 {
-	return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
+	return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL_ALL & ~I2C_FUNC_SMBUS_QUICK);
 }
 
 static const struct i2c_algorithm qup_i2c_algo = {

index 3eafe0eb3e4c..62a903fbe912 100644
@@ -781,7 +781,7 @@ static int s3c24xx_i2c_xfer(struct i2c_adapter *adap,
 /* declare our i2c functionality */
 static u32 s3c24xx_i2c_func(struct i2c_adapter *adap)
 {
-	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_NOSTART |
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL_ALL | I2C_FUNC_NOSTART |
 		I2C_FUNC_PROTOCOL_MANGLING;
 }