Re: [PATCH] rtc-ds1307: True SMBus compatibility

[Ed Swierk]

Here is an updated patch for rtc-ds1307 that allows the driver to work
with SMBus controllers like nforce2 that do not support i2c block
transfers.  The driver now checks the capabilities of the controller and
emulates the block transfers with SMBus byte transfers only if
necessary.

Signed-off-by: Ed Swierk <eswierk@xxxxxxxxxxxxxxxxxx>

Index: linux-2.6.27.4/drivers/rtc/rtc-ds1307.c
===================================================================
--- linux-2.6.27.4.orig/drivers/rtc/rtc-ds1307.c
+++ linux-2.6.27.4/drivers/rtc/rtc-ds1307.c
@@ -94,6 +94,10 @@ struct ds1307 {
 	struct i2c_client	*client;
 	struct rtc_device	*rtc;
 	struct work_struct	work;
+	s32 (*read_block_data)(struct i2c_client *client, u8 command,
+			       u8 length, u8 *values);
+	s32 (*write_block_data)(struct i2c_client *client, u8 command,
+				u8 length, const u8 *values);
 };
 
 struct chip_desc {
@@ -132,6 +136,61 @@ MODULE_DEVICE_TABLE(i2c, ds1307_id);
 
 /*----------------------------------------------------------------------*/
 
+static s32 ds1307_read_block_data_once(struct i2c_client *client, u8 command,
+				  u8 length, u8 *values)
+{
+	s32 i, data;
+	for (i = 0; i < length; i++) {
+		data = i2c_smbus_read_byte_data(client, command + i);
+		if (data < 0)
+			return data;
+		*(values + i) = data;
+	}
+	return i;
+}
+
+static s32 ds1307_read_block_data(struct i2c_client *client, u8 command,
+				  u8 length, u8 *values)
+{
+	u8 oldvalues[I2C_SMBUS_BLOCK_MAX];
+	s32 ret;
+	pr_debug("ds1307_read_block_data (length=%d)\n", length);
+	ret = ds1307_read_block_data_once(client, command, length, values);
+	if (ret < 0)
+		return ret;
+	do {
+		s32 ret;
+		memcpy(oldvalues, values, length);
+		ret = ds1307_read_block_data_once(client, command, length, values);
+		if (ret < 0)
+			return ret;
+	} while (memcmp(oldvalues, values, length));
+	return length;
+}
+
+static s32 ds1307_write_block_data(struct i2c_client *client, u8 command,
+				   u8 length, const u8 *values)
+{
+	u8 currvalues[I2C_SMBUS_BLOCK_MAX];
+	pr_debug("ds1307_write_block_data (length=%d)\n", length);
+	do {
+		s32 i, ret;
+		for (i = 0; i < length; i++) {
+			ret = i2c_smbus_write_byte_data(client, command + i,
+							*(values + i));
+			if (ret < 0)
+				return ret;
+		}
+		ret = ds1307_read_block_data_once(client, command, length,
+						  currvalues);
+		if (ret < 0)
+			return ret;
+	} while (memcmp(currvalues, values, length));
+	return length;
+}
+
+/*----------------------------------------------------------------------*/
+
 /*
  * The IRQ logic includes a "real" handler running in IRQ context just
  * long enough to schedule this workqueue entry.   We need a task context
@@ -202,7 +261,7 @@ static int ds1307_get_time(struct device
 	int		tmp;
 
 	/* read the RTC date and time registers all at once */
-	tmp = i2c_smbus_read_i2c_block_data(ds1307->client,
+	tmp = ds1307->read_block_data(ds1307->client,
 		DS1307_REG_SECS, 7, ds1307->regs);
 	if (tmp != 7) {
 		dev_err(dev, "%s error %d\n", "read", tmp);
@@ -279,7 +338,7 @@ static int ds1307_set_time(struct device
 		"write", buf[0], buf[1], buf[2], buf[3],
 		buf[4], buf[5], buf[6]);
 
-	result = i2c_smbus_write_i2c_block_data(ds1307->client, 0, 7, buf);
+	result = ds1307->write_block_data(ds1307->client, 0, 7, buf);
 	if (result < 0) {
 		dev_err(dev, "%s error %d\n", "write", result);
 		return result;
@@ -297,7 +356,7 @@ static int ds1307_read_alarm(struct devi
 		return -EINVAL;
 
 	/* read all ALARM1, ALARM2, and status registers at once */
-	ret = i2c_smbus_read_i2c_block_data(client,
+	ret = ds1307->read_block_data(client,
 			DS1339_REG_ALARM1_SECS, 9, ds1307->regs);
 	if (ret != 9) {
 		dev_err(dev, "%s error %d\n", "alarm read", ret);
@@ -356,7 +415,7 @@ static int ds1307_set_alarm(struct devic
 		t->enabled, t->pending);
 
 	/* read current status of both alarms and the chip */
-	ret = i2c_smbus_read_i2c_block_data(client,
+	ret = ds1307->read_block_data(client,
 			DS1339_REG_ALARM1_SECS, 9, buf);
 	if (ret != 9) {
 		dev_err(dev, "%s error %d\n", "alarm write", ret);
@@ -391,7 +450,7 @@ static int ds1307_set_alarm(struct devic
 	}
 	buf[8] = status & ~(DS1337_BIT_A1I | DS1337_BIT_A2I);
 
-	ret = i2c_smbus_write_i2c_block_data(client,
+	ret = ds1307->write_block_data(client,
 			DS1339_REG_ALARM1_SECS, 9, buf);
 	if (ret < 0) {
 		dev_err(dev, "can't set alarm time\n");
@@ -479,7 +538,7 @@ ds1307_nvram_read(struct kobject *kobj, 
 	if (unlikely(!count))
 		return count;
 
-	result = i2c_smbus_read_i2c_block_data(client, 8 + off, count, buf);
+	result = ds1307->read_block_data(client, 8 + off, count, buf);
 	if (result < 0)
 		dev_err(&client->dev, "%s error %d\n", "nvram read", result);
 	return result;
@@ -490,9 +549,11 @@ ds1307_nvram_write(struct kobject *kobj,
 		char *buf, loff_t off, size_t count)
 {
 	struct i2c_client	*client;
+	struct ds1307		*ds1307;
 	int			result;
 
 	client = kobj_to_i2c_client(kobj);
+	ds1307 = i2c_get_clientdata(client);
 
 	if (unlikely(off >= NVRAM_SIZE))
 		return -EFBIG;
@@ -501,7 +562,7 @@ ds1307_nvram_write(struct kobject *kobj,
 	if (unlikely(!count))
 		return count;
 
-	result = i2c_smbus_write_i2c_block_data(client, 8 + off, count, buf);
+	result = ds1307->write_block_data(client, 8 + off, count, buf);
 	if (result < 0) {
 		dev_err(&client->dev, "%s error %d\n", "nvram write", result);
 		return result;
@@ -536,9 +597,8 @@ static int __devinit ds1307_probe(struct
 	int			want_irq = false;
 	unsigned char		*buf;
 
-	if (!i2c_check_functionality(adapter,
-			I2C_FUNC_SMBUS_WRITE_BYTE_DATA |
-			I2C_FUNC_SMBUS_I2C_BLOCK))
+	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA)
+	    && !i2c_check_functionality(adapter, I2C_FUNC_SMBUS_I2C_BLOCK))
 		return -EIO;
 
 	if (!(ds1307 = kzalloc(sizeof(struct ds1307), GFP_KERNEL)))
@@ -548,6 +608,14 @@ static int __devinit ds1307_probe(struct
 	i2c_set_clientdata(client, ds1307);
 	ds1307->type = id->driver_data;
 	buf = ds1307->regs;
+	if (i2c_check_functionality(adapter, I2C_FUNC_SMBUS_I2C_BLOCK)) {
+		ds1307->read_block_data = i2c_smbus_read_i2c_block_data;
+		ds1307->write_block_data = i2c_smbus_write_i2c_block_data;
+	}
+	else {
+		ds1307->read_block_data = ds1307_read_block_data;
+		ds1307->write_block_data = ds1307_write_block_data;
+	}
 
 	switch (ds1307->type) {
 	case ds_1337:
@@ -558,7 +626,7 @@ static int __devinit ds1307_probe(struct
 			want_irq = true;
 		}
 		/* get registers that the "rtc" read below won't read... */
-		tmp = i2c_smbus_read_i2c_block_data(ds1307->client,
+		tmp = ds1307->read_block_data(ds1307->client,
 				DS1337_REG_CONTROL, 2, buf);
 		if (tmp != 2) {
 			pr_debug("read error %d\n", tmp);
@@ -596,7 +664,7 @@ static int __devinit ds1307_probe(struct
 
 read_rtc:
 	/* read RTC registers */
-	tmp = i2c_smbus_read_i2c_block_data(ds1307->client, 0, 8, buf);
+	tmp = ds1307->read_block_data(ds1307->client, 0, 8, buf);
 	if (tmp != 8) {
 		pr_debug("read error %d\n", tmp);
 		err = -EIO;