Date:	Sun, 11 May 2008 02:59:34 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Jean Delvare <khali@...ux-fr.org>
cc:	David Brownell <david-b@...bell.net>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Alexander Bigga <ab@...able.de>,
	Atsushi Nemoto <anemo@....ocn.ne.jp>, i2c@...sensors.org,
	rtc-linux@...glegroups.com, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 4/4] RTC: SMBus support for the M41T80

Hi Jean,

> OK, I've just spent some time trying to improve this piece of
> documentation. I'll send it to you and the i2c list in a moment, to not
> overload this thread. Please tell me if my proposed changes make the
> document clearer.

 Certainly.

> I don't understand why you insist on having a single m41t80_transfer()
> function for read and write transactions, when the read and write cases
> share zero code. Separate functions would perform better.

 Nothing to understand here and I do not insist on anything.  You are
right of course -- I must have got too much influenced by i2c_transfer()  
and have not thought of splitting.

> Still not correct, sorry. The driver is still making unconditional
> calls to i2c_smbus_read_byte_data() and i2c_smbus_write_byte_data(), so
> the underlying adapter _must_ support I2C_FUNC_SMBUS_READ_BYTE_DATA and
> I2C_FUNC_SMBUS_WRITE_BYTE_DATA (i.e. I2C_FUNC_SMBUS_BYTE_DATA), even if

 Well, as I understand the support for I2C_FUNC_SMBUS_I2C_BLOCK
(read/write, as appropriate) implies I2C_FUNC_SMBUS_BYTE_DATA as the
latter is a special case of the former, where the length of the transfer
equals one.  But I agree -- in the light of what you wrote previously a
bus adapter that supports say I2C_FUNC_SMBUS_READ_I2C_BLOCK is meant to
have I2C_FUNC_SMBUS_READ_BYTE set as well, so no need to check for it
here.

 If we agree on this one, I will retest and submit the whole batch again,
updated as needed.

  Maciej

patch-2.6.26-rc1-20080505-m41t80-smbus-16
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-m41t80.c linux-2.6.26-rc1-20080505/drivers/rtc/rtc-m41t80.c
--- linux-2.6.26-rc1-20080505.macro/drivers/rtc/rtc-m41t80.c	2008-05-05 02:55:40.000000000 +0000
+++ linux-2.6.26-rc1-20080505/drivers/rtc/rtc-m41t80.c	2008-05-11 00:16:36.000000000 +0000
@@ -6,6 +6,7 @@
  * Based on m41t00.c by Mark A. Greer <mgreer@...sta.com>
  *
  * 2006 (c) mycable GmbH
+ * Copyright (c) 2008  Maciej W. Rozycki
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -36,6 +37,8 @@
 #define M41T80_REG_DAY	5
 #define M41T80_REG_MON	6
 #define M41T80_REG_YEAR	7
+#define M41T80_REG_CONTROL	8
+#define M41T80_REG_WATCHDOG	9
 #define M41T80_REG_ALARM_MON	0xa
 #define M41T80_REG_ALARM_DAY	0xb
 #define M41T80_REG_ALARM_HOUR	0xc
@@ -58,7 +61,7 @@
 #define M41T80_FEATURE_HT	(1 << 0)
 #define M41T80_FEATURE_BL	(1 << 1)
 
-#define DRV_VERSION "0.05"
+#define DRV_VERSION "0.06"
 
 static const struct i2c_device_id m41t80_id[] = {
 	{ "m41t80", 0 },
@@ -78,31 +81,83 @@ struct m41t80_data {
 	struct rtc_device *rtc;
 };
 
-static int m41t80_get_datetime(struct i2c_client *client,
-			       struct rtc_time *tm)
+
+static int m41t80_write_block_data(struct i2c_client *client,
+				   u8 reg, u8 num, u8 *buf)
 {
-	u8 buf[M41T80_DATETIME_REG_SIZE], dt_addr[1] = { M41T80_REG_SEC };
-	struct i2c_msg msgs[] = {
-		{
-			.addr	= client->addr,
-			.flags	= 0,
-			.len	= 1,
-			.buf	= dt_addr,
-		},
-		{
-			.addr	= client->addr,
-			.flags	= I2C_M_RD,
-			.len	= M41T80_DATETIME_REG_SIZE - M41T80_REG_SEC,
-			.buf	= buf + M41T80_REG_SEC,
-		},
-	};
+	int i, rc;
 
-	if (i2c_transfer(client->adapter, msgs, 2) < 0) {
-		dev_err(&client->dev, "read error\n");
-		return -EIO;
+	if (i2c_check_functionality(client->adapter,
+				    I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
+		i = i2c_smbus_write_i2c_block_data(client, reg, num, buf);
+	} else {
+		for (i = 0; i < num; i++) {
+			rc = i2c_smbus_write_byte_data(client, reg + i,
+						       buf[i]);
+			if (rc < 0) {
+				i = rc;
+				goto out;
+			}
+		}
 	}
+out:
+	return i;
+}
+
+static int m41t80_read_block_data(struct i2c_client *client,
+				  u8 reg, u8 num, u8 *buf)
+{
+	int i, rc;
+
+	if (i2c_check_functionality(client->adapter,
+				    I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
+		i = i2c_smbus_read_i2c_block_data(client, reg, num, buf);
+	} else {
+		for (i = 0; i < num; i++) {
+			rc = i2c_smbus_read_byte_data(client, reg + i);
+			if (rc < 0) {
+				i = rc;
+				goto out;
+			}
+			buf[i] = rc;
+		}
+	}
+out:
+	return i;
+}
+
+static int m41t80_get_datetime(struct i2c_client *client, struct rtc_time *tm)
+{
+	u8 buf[M41T80_DATETIME_REG_SIZE];
+	int loops = 2;
+	int sec0, sec1;
+
+	/*
+	 * Time registers are latched by this chip if an I2C block
+	 * transfer is used, but with SMBus-style byte accesses
+	 * this is not the case, so check seconds for a wraparound.
+	 */
+	do {
+		if (m41t80_read_block_data(client, M41T80_REG_SEC,
+					   M41T80_DATETIME_REG_SIZE -
+					   M41T80_REG_SEC,
+					   buf + M41T80_REG_SEC) < 0) {
+			dev_err(&client->dev, "read error\n");
+			return -EIO;
+		}
+		sec0 = buf[M41T80_REG_SEC];
+
+		sec1 = i2c_smbus_read_byte_data(client, M41T80_REG_SEC);
+		if (sec1 < 0) {
+			dev_err(&client->dev, "read error\n");
+			return -EIO;
+		}
 
-	tm->tm_sec = BCD2BIN(buf[M41T80_REG_SEC] & 0x7f);
+		sec0 = BCD2BIN(sec0 & 0x7f);
+		sec1 = BCD2BIN(sec1 & 0x7f);
+	} while (sec1 < sec0 && --loops);
+
+	tm->tm_sec = sec1;
 	tm->tm_min = BCD2BIN(buf[M41T80_REG_MIN] & 0x7f);
 	tm->tm_hour = BCD2BIN(buf[M41T80_REG_HOUR] & 0x3f);
 	tm->tm_mday = BCD2BIN(buf[M41T80_REG_DAY] & 0x3f);
@@ -117,39 +172,16 @@ static int m41t80_get_datetime(struct i2
 /* Sets the given date and time to the real time clock. */
 static int m41t80_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 {
-	u8 wbuf[1 + M41T80_DATETIME_REG_SIZE];
-	u8 *buf = &wbuf[1];
-	u8 dt_addr[1] = { M41T80_REG_SEC };
-	struct i2c_msg msgs_in[] = {
-		{
-			.addr	= client->addr,
-			.flags	= 0,
-			.len	= 1,
-			.buf	= dt_addr,
-		},
-		{
-			.addr	= client->addr,
-			.flags	= I2C_M_RD,
-			.len	= M41T80_DATETIME_REG_SIZE - M41T80_REG_SEC,
-			.buf	= buf + M41T80_REG_SEC,
-		},
-	};
-	struct i2c_msg msgs[] = {
-		{
-			.addr	= client->addr,
-			.flags	= 0,
-			.len	= 1 + M41T80_DATETIME_REG_SIZE,
-			.buf	= wbuf,
-		 },
-	};
+	u8 buf[M41T80_DATETIME_REG_SIZE];
 
 	/* Read current reg values into buf[1..7] */
-	if (i2c_transfer(client->adapter, msgs_in, 2) < 0) {
+	if (m41t80_read_block_data(client, M41T80_REG_SEC,
+				   M41T80_DATETIME_REG_SIZE - M41T80_REG_SEC,
+				   buf + M41T80_REG_SEC) < 0) {
 		dev_err(&client->dev, "read error\n");
 		return -EIO;
 	}
 
-	wbuf[0] = 0; /* offset into rtc's regs */
 	/* Merge time-data and register flags into buf[0..7] */
 	buf[M41T80_REG_SSEC] = 0;
 	buf[M41T80_REG_SEC] =
@@ -167,7 +199,8 @@ static int m41t80_set_datetime(struct i2
 	/* assume 20YY not 19YY */
 	buf[M41T80_REG_YEAR] = BIN2BCD(tm->tm_year % 100);
 
-	if (i2c_transfer(client->adapter, msgs, 1) != 1) {
+	if (m41t80_write_block_data(client, M41T80_REG_SSEC,
+				    M41T80_DATETIME_REG_SIZE, buf) < 0) {
 		dev_err(&client->dev, "write error\n");
 		return -EIO;
 	}
@@ -241,34 +274,11 @@ err:
 static int m41t80_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *t)
 {
 	struct i2c_client *client = to_i2c_client(dev);
-	u8 wbuf[1 + M41T80_ALARM_REG_SIZE];
-	u8 *buf = &wbuf[1];
+	u8 buf[M41T80_ALARM_REG_SIZE];
 	u8 *reg = buf - M41T80_REG_ALARM_MON;
-	u8 dt_addr[1] = { M41T80_REG_ALARM_MON };
-	struct i2c_msg msgs_in[] = {
-		{
-			.addr	= client->addr,
-			.flags	= 0,
-			.len	= 1,
-			.buf	= dt_addr,
-		},
-		{
-			.addr	= client->addr,
-			.flags	= I2C_M_RD,
-			.len	= M41T80_ALARM_REG_SIZE,
-			.buf	= buf,
-		},
-	};
-	struct i2c_msg msgs[] = {
-		{
-			.addr	= client->addr,
-			.flags	= 0,
-			.len	= 1 + M41T80_ALARM_REG_SIZE,
-			.buf	= wbuf,
-		 },
-	};
 
-	if (i2c_transfer(client->adapter, msgs_in, 2) < 0) {
+	if (m41t80_read_block_data(client, M41T80_REG_ALARM_MON,
+				   M41T80_ALARM_REG_SIZE, buf) < 0) {
 		dev_err(&client->dev, "read error\n");
 		return -EIO;
 	}
@@ -278,7 +288,6 @@ static int m41t80_rtc_set_alarm(struct d
 	reg[M41T80_REG_ALARM_MIN] = 0;
 	reg[M41T80_REG_ALARM_SEC] = 0;
 
-	wbuf[0] = M41T80_REG_ALARM_MON; /* offset into rtc's regs */
 	reg[M41T80_REG_ALARM_SEC] |= t->time.tm_sec >= 0 ?
 		BIN2BCD(t->time.tm_sec) : 0x80;
 	reg[M41T80_REG_ALARM_MIN] |= t->time.tm_min >= 0 ?
@@ -292,7 +301,8 @@ static int m41t80_rtc_set_alarm(struct d
 	else
 		reg[M41T80_REG_ALARM_DAY] |= 0x40;
 
-	if (i2c_transfer(client->adapter, msgs, 1) != 1) {
+	if (m41t80_write_block_data(client, M41T80_REG_ALARM_MON,
+				    M41T80_ALARM_REG_SIZE, buf) < 0) {
 		dev_err(&client->dev, "write error\n");
 		return -EIO;
 	}
@@ -312,24 +322,10 @@ static int m41t80_rtc_read_alarm(struct 
 {
 	struct i2c_client *client = to_i2c_client(dev);
 	u8 buf[M41T80_ALARM_REG_SIZE + 1]; /* all alarm regs and flags */
-	u8 dt_addr[1] = { M41T80_REG_ALARM_MON };
 	u8 *reg = buf - M41T80_REG_ALARM_MON;
-	struct i2c_msg msgs[] = {
-		{
-			.addr	= client->addr,
-			.flags	= 0,
-			.len	= 1,
-			.buf	= dt_addr,
-		},
-		{
-			.addr	= client->addr,
-			.flags	= I2C_M_RD,
-			.len	= M41T80_ALARM_REG_SIZE + 1,
-			.buf	= buf,
-		},
-	};
 
-	if (i2c_transfer(client->adapter, msgs, 2) < 0) {
+	if (m41t80_read_block_data(client, M41T80_REG_ALARM_MON,
+				   M41T80_ALARM_REG_SIZE + 1, buf) < 0) {
 		dev_err(&client->dev, "read error\n");
 		return -EIO;
 	}
@@ -488,26 +484,16 @@ static int boot_flag;
  */
 static void wdt_ping(void)
 {
-	unsigned char i2c_data[2];
-	struct i2c_msg msgs1[1] = {
-		{
-			.addr	= save_client->addr,
-			.flags	= 0,
-			.len	= 2,
-			.buf	= i2c_data,
-		},
-	};
-	i2c_data[0] = 0x09;		/* watchdog register */
+	u8 wdt = 0x80;				/* WDS = 1 (0x80)  */
 
 	if (wdt_margin > 31)
-		i2c_data[1] = (wdt_margin & 0xFC) | 0x83; /* resolution = 4s */
+		/* mulitplier = WD_TIMO / 4, resolution = 4s (0x3)  */
+		wdt |= (wdt_margin & 0xfc) | 0x3;
 	else
-		/*
-		 * WDS = 1 (0x80), mulitplier = WD_TIMO, resolution = 1s (0x02)
-		 */
-		i2c_data[1] = wdt_margin<<2 | 0x82;
+		/* mulitplier = WD_TIMO, resolution = 1s (0x2)  */
+		wdt |= wdt_margin << 2 | 0x2;
 
-	i2c_transfer(save_client->adapter, msgs1, 1);
+	i2c_smbus_write_byte_data(save_client, M41T80_REG_WATCHDOG, wdt);
 }
 
 /**
@@ -517,36 +503,8 @@ static void wdt_ping(void)
  */
 static void wdt_disable(void)
 {
-	unsigned char i2c_data[2], i2c_buf[0x10];
-	struct i2c_msg msgs0[2] = {
-		{
-			.addr	= save_client->addr,
-			.flags	= 0,
-			.len	= 1,
-			.buf	= i2c_data,
-		},
-		{
-			.addr	= save_client->addr,
-			.flags	= I2C_M_RD,
-			.len	= 1,
-			.buf	= i2c_buf,
-		},
-	};
-	struct i2c_msg msgs1[1] = {
-		{
-			.addr	= save_client->addr,
-			.flags	= 0,
-			.len	= 2,
-			.buf	= i2c_data,
-		},
-	};
-
-	i2c_data[0] = 0x09;
-	i2c_transfer(save_client->adapter, msgs0, 2);
-
-	i2c_data[0] = 0x09;
-	i2c_data[1] = 0x00;
-	i2c_transfer(save_client->adapter, msgs1, 1);
+	i2c_smbus_read_byte_data(save_client, M41T80_REG_WATCHDOG);
+	i2c_smbus_write_byte_data(save_client, M41T80_REG_WATCHDOG, 0);
 }
 
 /**
@@ -736,13 +694,21 @@ static int m41t80_probe(struct i2c_clien
 	struct rtc_device *rtc = NULL;
 	struct rtc_time tm;
 	struct m41t80_data *clientdata = NULL;
+	int reg;
 
-	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C
-				     | I2C_FUNC_SMBUS_BYTE_DATA)) {
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_BYTE_DATA)) {
 		rc = -ENODEV;
 		goto exit;
 	}
 
+	/* Trivially check it's there; keep the result for the HT check. */
+	reg = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_HOUR);
+	if (reg < 0) {
+		rc = -ENXIO;
+		goto exit;
+	}
+
 	dev_info(&client->dev,
 		 "chip found, driver version " DRV_VERSION "\n");
 
@@ -765,11 +731,7 @@ static int m41t80_probe(struct i2c_clien
 	i2c_set_clientdata(client, clientdata);
 
 	/* Make sure HT (Halt Update) bit is cleared */
-	rc = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_HOUR);
-	if (rc < 0)
-		goto ht_err;
-
-	if (rc & M41T80_ALHOUR_HT) {
+	if (reg & M41T80_ALHOUR_HT) {
 		if (clientdata->features & M41T80_FEATURE_HT) {
 			m41t80_get_datetime(client, &tm);
 			dev_info(&client->dev, "HT bit was set!\n");
@@ -782,18 +744,18 @@ static int m41t80_probe(struct i2c_clien
 		}
 		if (i2c_smbus_write_byte_data(client,
 					      M41T80_REG_ALARM_HOUR,
-					      rc & ~M41T80_ALHOUR_HT) < 0)
+					      reg & ~M41T80_ALHOUR_HT) < 0)
 			goto ht_err;
 	}
 
 	/* Make sure ST (stop) bit is cleared */
-	rc = i2c_smbus_read_byte_data(client, M41T80_REG_SEC);
-	if (rc < 0)
+	reg = i2c_smbus_read_byte_data(client, M41T80_REG_SEC);
+	if (reg < 0)
 		goto st_err;
 
-	if (rc & M41T80_SEC_ST) {
+	if (reg & M41T80_SEC_ST) {
 		if (i2c_smbus_write_byte_data(client, M41T80_REG_SEC,
-					      rc & ~M41T80_SEC_ST) < 0)
+					      reg & ~M41T80_SEC_ST) < 0)
 			goto st_err;
 	}
 
--
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