[PATCH v2] i2c: stub: Add support for SMBus block commands

[Guenter Roeck]

SMBus block commands are different to I2C block commands since
the returned data is not normally accessible with byte or word
commands on other command offsets. Add linked list of 'block'
commands to support those commands.

Access mechanism is quite simple: Block commands must be written
before they can be read. The first write selects the block length.
Subsequent writes can be partial. Block read commands always return
the number of bytes selected with the first write.

Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
v2: Make new functionality only available on request via functionality
    module parameter
    Add more details about SMBus block mode support to documentation
    Use correct sizeof() variable in devm_kzalloc
    Use stub_find_block() only in SMBus block command itself.
    Store first word of block data in chip->words[].
    When writing block data and the written data is longer than
    the first write, bail out with debug message indicating the reason
    for the error.

 Documentation/i2c/i2c-stub |  9 ++++-
 drivers/i2c/i2c-stub.c     | 99 +++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 101 insertions(+), 7 deletions(-)

diff --git a/Documentation/i2c/i2c-stub b/Documentation/i2c/i2c-stub
index fa4b669..531510b 100644
--- a/Documentation/i2c/i2c-stub
+++ b/Documentation/i2c/i2c-stub
@@ -2,9 +2,9 @@ MODULE: i2c-stub
 
 DESCRIPTION:
 
-This module is a very simple fake I2C/SMBus driver.  It implements five
+This module is a very simple fake I2C/SMBus driver.  It implements six
 types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
-word data, and (r/w) I2C block data.
+word data, (r/w) I2C block data, and (r/w) SMBus block data.
 
 You need to provide chip addresses as a module parameter when loading this
 driver, which will then only react to SMBus commands to these addresses.
@@ -19,6 +19,11 @@ A pointer register with auto-increment is implemented for all byte
 operations.  This allows for continuous byte reads like those supported by
 EEPROMs, among others.
 
+SMBus block commands must be written to configure an SMBus command for
+SMBus block operations. The first SMBus block write selects the block length.
+Subsequent writes can be partial. Block read commands always return
+the number of bytes selected with the first write.
+
 The typical use-case is like this:
 	1. load this module
 	2. use i2cset (from the i2c-tools project) to pre-load some data
diff --git a/drivers/i2c/i2c-stub.c b/drivers/i2c/i2c-stub.c
index 77e4849..4fbe565 100644
--- a/drivers/i2c/i2c-stub.c
+++ b/drivers/i2c/i2c-stub.c
@@ -27,29 +27,64 @@
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/i2c.h>
+#include <linux/list.h>
 
 #define MAX_CHIPS 10
-#define STUB_FUNC (I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | \
-		   I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | \
-		   I2C_FUNC_SMBUS_I2C_BLOCK)
+#define STUB_FUNC_DEFAULT \
+		(I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | \
+		 I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | \
+		 I2C_FUNC_SMBUS_I2C_BLOCK)
+
+#define STUB_FUNC_ALL \
+		(STUB_FUNC_DEFAULT | I2C_FUNC_SMBUS_BLOCK_DATA)
 
 static unsigned short chip_addr[MAX_CHIPS];
 module_param_array(chip_addr, ushort, NULL, S_IRUGO);
 MODULE_PARM_DESC(chip_addr,
 		 "Chip addresses (up to 10, between 0x03 and 0x77)");
 
-static unsigned long functionality = STUB_FUNC;
+static unsigned long functionality = STUB_FUNC_DEFAULT;
 module_param(functionality, ulong, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(functionality, "Override functionality bitfield");
 
+struct smbus_block_data {
+	struct list_head node;
+	u8 command;
+	u8 len;
+	u8 block[I2C_SMBUS_BLOCK_MAX];
+};
+
 struct stub_chip {
 	u8 pointer;
 	u16 words[256];		/* Byte operations use the LSB as per SMBus
 				   specification */
+	struct list_head smbus_blocks;
 };
 
 static struct stub_chip *stub_chips;
 
+static struct smbus_block_data *stub_find_block(struct device *dev,
+						struct stub_chip *chip,
+						u8 command, bool create)
+{
+	struct smbus_block_data *b, *rb = NULL;
+
+	list_for_each_entry(b, &chip->smbus_blocks, node) {
+		if (b->command == command) {
+			rb = b;
+			break;
+		}
+	}
+	if (rb == NULL && create) {
+		rb = devm_kzalloc(dev, sizeof(*rb), GFP_KERNEL);
+		if (rb == NULL)
+			return rb;
+		rb->command = command;
+		list_add(&rb->node, &chip->smbus_blocks);
+	}
+	return rb;
+}
+
 /* Return negative errno on error. */
 static s32 stub_xfer(struct i2c_adapter *adap, u16 addr, unsigned short flags,
 	char read_write, u8 command, int size, union i2c_smbus_data *data)
@@ -57,6 +92,7 @@ static s32 stub_xfer(struct i2c_adapter *adap, u16 addr, unsigned short flags,
 	s32 ret;
 	int i, len;
 	struct stub_chip *chip = NULL;
+	struct smbus_block_data *b;
 
 	/* Search for the right chip */
 	for (i = 0; i < MAX_CHIPS && chip_addr[i]; i++) {
@@ -148,6 +184,57 @@ static s32 stub_xfer(struct i2c_adapter *adap, u16 addr, unsigned short flags,
 		ret = 0;
 		break;
 
+	case I2C_SMBUS_BLOCK_DATA:
+		b = stub_find_block(&adap->dev, chip, command, false);
+		if (read_write == I2C_SMBUS_WRITE) {
+			len = data->block[0];
+			if (len == 0 || len > I2C_SMBUS_BLOCK_MAX) {
+				ret = -EINVAL;
+				break;
+			}
+			if (b && len > b->len) {
+				dev_dbg(&adap->dev,
+					"Attempt to write more data (%d) than with initial SMBus block write (%d)\n",
+					len, b->len);
+				ret = -EINVAL;
+				break;
+			}
+			if (b == NULL) {
+				b = stub_find_block(&adap->dev, chip, command,
+						    true);
+				if (b == NULL) {
+					ret = -ENOMEM;
+					break;
+				}
+				/* First write sets block length */
+				b->len = len;
+			}
+			for (i = 0; i < len; i++)
+				b->block[i] = data->block[i + 1];
+			/* update for byte and word commands */
+			chip->words[command] = (b->block[0] << 8) | b->len;
+			dev_dbg(&adap->dev,
+				"smbus block data - addr 0x%02x, wrote %d bytes at 0x%02x.\n",
+				addr, len, command);
+		} else {
+			if (b == NULL) {
+				dev_dbg(&adap->dev,
+					"SMBus block read command without prior block write not supported\n");
+				ret = -EOPNOTSUPP;
+				break;
+			}
+			len = b->len;
+			data->block[0] = len;
+			for (i = 0; i < len; i++)
+				data->block[i + 1] = b->block[i];
+			dev_dbg(&adap->dev,
+				"smbus block data - addr 0x%02x, read  %d bytes at 0x%02x.\n",
+				addr, len, command);
+		}
+
+		ret = 0;
+		break;
+
 	default:
 		dev_dbg(&adap->dev, "Unsupported I2C/SMBus command\n");
 		ret = -EOPNOTSUPP;
@@ -159,7 +246,7 @@ static s32 stub_xfer(struct i2c_adapter *adap, u16 addr, unsigned short flags,
 
 static u32 stub_func(struct i2c_adapter *adapter)
 {
-	return STUB_FUNC & functionality;
+	return STUB_FUNC_ALL & functionality;
 }
 
 static const struct i2c_algorithm smbus_algorithm = {
@@ -199,6 +286,8 @@ static int __init i2c_stub_init(void)
 		pr_err("i2c-stub: Out of memory\n");
 		return -ENOMEM;
 	}
+	for (i--; i >= 0; i--)
+		INIT_LIST_HEAD(&stub_chips[i].smbus_blocks);
 
 	ret = i2c_add_adapter(&stub_adapter);
 	if (ret)
-- 
1.9.1

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