Re: [RFC][PATCH 4/4] RTC: SMBus support for the M41T80

Maciej W. Rozycki
2008-05-11T01:59:34Z

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@mvista.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;
}