[PATCH] rtc-ds1307: True SMBus compatibility

[Ed Swierk <eswierk-BGArkANP9klv6pq1l3V1OdBPR1lH4CV8@public.gmane.org>]

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[Resent to correct linux-i2c address]

Following up to Sebastien Barre's recent patch, here I go one step
further, replacing i2c block transfers with SMBus byte transfers.
Sticking to pure SMBus makes the driver work on our board, which has an
nVidia SMBus controller driving a DS1339; nforce2 controllers
unfortunately don't support any flavor of i2c block transfer.

Reading or writing registers repeatedly until they stick is rather
nauseating but I'm aiming for correctness if not elegance.  I would
appreciate any suggestions for improvement.

Signed-off-by: Ed Swierk <eswierk-BGArkANP9klv6pq1l3V1OdBPR1lH4CV8@public.gmane.org>


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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
@@ -132,6 +132,64 @@ 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];
+	s32 ret;
+	pr_debug("ds1307_write_block_data (length=%d)\n", length);
+	ret = ds1307_read_block_data_once(client, command, length, currvalues);
+	if (ret < 0)
+		return ret;
+	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 +266,7 @@ 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 +343,7 @@ 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 +361,7 @@ 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 +420,7 @@ 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 +455,7 @@ 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 +543,7 @@ 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;
@@ -501,7 +565,7 @@ 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;
@@ -537,8 +601,7 @@ static int __devinit ds1307_probe(struct
 	unsigned char		*buf;
 
 	if (!i2c_check_functionality(adapter,
-			I2C_FUNC_SMBUS_WRITE_BYTE_DATA |
-			I2C_FUNC_SMBUS_I2C_BLOCK))
+			I2C_FUNC_SMBUS_BYTE_DATA))
 		return -EIO;
 
 	if (!(ds1307 = kzalloc(sizeof(struct ds1307), GFP_KERNEL)))
@@ -558,7 +621,7 @@ 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 +659,7 @@ 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;