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Date: Thu, 08 May 2008 13:38:47 +0900 (JST)
From: Atsushi Nemoto <anemo@....ocn.ne.jp>
To: macro@...ux-mips.org
Cc: a.zummo@...ertech.it, khali@...ux-fr.org, ralf@...ux-mips.org,
tglx@...utronix.de, akpm@...ux-foundation.org,
rtc-linux@...glegroups.com, i2c@...sensors.org,
linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
ab@...able.de, mgreer@...sta.com
Subject: Re: [RFC][PATCH 4/4] RTC: SMBus support for the M41T80, etc. driver
Added CC to authers of the driver.
On Wed, 7 May 2008 01:40:41 +0100 (BST), "Maciej W. Rozycki" <macro@...ux-mips.org> wrote:
> The BCM1250A SOC which is used on the SWARM board utilising an M41T81
> chip only supports pure I2C in the raw bit-banged mode. Nobody sane
> really wants to use it unless absolutely necessary and the M41T80, etc.
> chips work just fine with an SMBus controller which is what the standard
> mode of operation of the BCM1250A. The only drawback of byte accesses
> with the M41T80 is the chip only latches clock data registers for the
> duration of an I2C transaction which works fine with a block transfers,
> but not byte-wise accesses.
>
> The driver currently requires an I2C controller providing both SMBus and
> pure I2C access. This is a set of changes to make it work with either,
> with a preference to pure I2C. The problem of unlatched clock data if
> SMBus transactions are used is resolved in the standard way.
>
> Whether a choice between SMBus and pure I2C access is possible is
> obviously device dependent. If the code proved useful for other I2C
> devices, then it could be moved to a more generic place. It is a code
> simplification regardless -- similar I2C packet definitions are not
> scattered throughout the driver anymore.
>
> Signed-off-by: Maciej W. Rozycki <macro@...ux-mips.org>
> ---
> Please note I have no means to test these changes with a pure I2C
> controller -- anybody interested, please help.
I tested this with i2c-gpio. It needs some fix. Detailed below.
> -static int m41t80_get_datetime(struct i2c_client *client,
> - struct rtc_time *tm)
> +
> +static int m41t80_i2c_transfer(struct i2c_client *client, int write,
> + 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,
> + .buf = ®,
> },
> {
> .addr = client->addr,
> - .flags = I2C_M_RD,
> - .len = M41T80_DATETIME_REG_SIZE - M41T80_REG_SEC,
> - .buf = buf + M41T80_REG_SEC,
> + .flags = write ? 0 : I2C_M_RD,
> + .len = num,
> + .buf = buf,
> },
> };
>
> - if (i2c_transfer(client->adapter, msgs, 2) < 0) {
> - dev_err(&client->dev, "read error\n");
> - return -EIO;
> + return i2c_transfer(client->adapter, msgs, 2);
> +}
For write transfer, you must use only one i2c_msg. If two i2c_msg
were used, the slave address is inserted between register number and
first data. This chip cannot accept such sequence.
> +static int m41t80_transfer(struct i2c_client *client, int write,
> + u8 reg, u8 num, u8 *buf)
> +{
> + int i, rc;
> +
> + if (i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> + return m41t80_i2c_transfer(client, write, reg, num, buf);
On success, m41t80_i2c_transfer() returns positive value, but
m41t80_transfer() should return 0.
Here is a proposed fix on top of your patch.
--- drivers/rtc/rtc-m41t80.c.orig 2008-05-08 11:08:57.000000000 +0900
+++ drivers/rtc/rtc-m41t80.c 2008-05-08 12:30:49.000000000 +0900
@@ -83,8 +83,8 @@ struct m41t80_data {
};
-static int m41t80_i2c_transfer(struct i2c_client *client, int write,
- u8 reg, u8 num, u8 *buf)
+static int m41t80_i2c_read_transfer(struct i2c_client *client,
+ u8 reg, u8 num, u8 *buf)
{
struct i2c_msg msgs[] = {
{
@@ -95,7 +95,7 @@ static int m41t80_i2c_transfer(struct i2
},
{
.addr = client->addr,
- .flags = write ? 0 : I2C_M_RD,
+ .flags = I2C_M_RD,
.len = num,
.buf = buf,
},
@@ -104,13 +104,29 @@ static int m41t80_i2c_transfer(struct i2
return i2c_transfer(client->adapter, msgs, 2);
}
+static int m41t80_i2c_write_transfer(struct i2c_client *client,
+ u8 reg, u8 num, u8 *buf)
+{
+ u8 wbuf[M41T80_DATETIME_REG_SIZE + 1];
+ struct i2c_msg msg = {
+ .addr = client->addr,
+ .flags = 0,
+ .len = num + 1,
+ .buf = wbuf,
+ };
+
+ wbuf[0] = reg;
+ memcpy(wbuf + 1, buf, num);
+ return i2c_transfer(client->adapter, &msg, 1);
+}
+
static int m41t80_read_byte_data(struct i2c_client *client, u8 reg)
{
int rc;
u8 val;
if (i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
- rc = m41t80_i2c_transfer(client, 0, reg, 1, &val);
+ rc = m41t80_i2c_read_transfer(client, reg, 1, &val);
if (rc < 0)
return rc;
else
@@ -122,7 +138,7 @@ static int m41t80_read_byte_data(struct
static int m41t80_write_byte_data(struct i2c_client *client, u8 reg, u8 val)
{
if (i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
- return m41t80_i2c_transfer(client, 1, reg, 1, &val);
+ return m41t80_i2c_write_transfer(client, reg, 1, &val);
else
return i2c_smbus_write_byte_data(client, reg, val);
}
@@ -132,16 +148,20 @@ static int m41t80_transfer(struct i2c_cl
{
int i, rc;
- if (i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
- return m41t80_i2c_transfer(client, write, reg, num, buf);
- else if (write) {
+ if (i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
+ if (write)
+ rc = m41t80_i2c_write_transfer(client, reg, num, buf);
+ else
+ rc = m41t80_i2c_read_transfer(client, reg, num, buf);
+ if (rc < 0)
+ return rc;
+ } else if (write) {
for (i = 0; i < num; i++) {
rc = i2c_smbus_write_byte_data(client, reg + i,
buf[i]);
if (rc < 0)
return rc;
}
- return 0;
} else {
for (i = 0; i < num; i++) {
rc = i2c_smbus_read_byte_data(client, reg + i);
@@ -149,8 +169,8 @@ static int m41t80_transfer(struct i2c_cl
return rc;
buf[i] = rc;
}
- return 0;
}
+ return 0;
}
static int m41t80_get_datetime(struct i2c_client *client, struct rtc_time *tm)
--
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