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Subject[RFC] Driver for Real Time Clock chip ST M41T65
I will be using a Real Time Clock chip, ST M41T65, on a new embedded system.
The chip is quite similar to the M41T8x family, which already has driver
rtc-m41t80.c.

Would it be more acceptible to generalize rtc-m41t80.c (perhaps renaming it to
rtc-m41txx.c) or would it be better to create a new rtc-m41t6x.c?

The main differences I see between the M41T65 and M41T80 are that:

1) The M41T65 watchdog timer has three bits controlling resolution (versus two
for the M41T80).

2) There is no register 0x13 for controlling square-wave output.

Here is the patch I am currently using (on some prototype hardware), for
reference. I've introduced two new feature bits to cover the above
differences. I have not yet done any renaming, nor have I modified any of the
defconfigs to account for a name change.

Steve Falco
sfalco@harris.com

diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index a3e0880..4d9b1a9 100644
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -58,18 +58,21 @@

#define M41T80_FEATURE_HT (1 << 0)
#define M41T80_FEATURE_BL (1 << 1)
+#define M41T80_FEATURE_SQ (1 << 2)
+#define M41T80_FEATURE_WD (1 << 3)

#define DRV_VERSION "0.05"

static const struct i2c_device_id m41t80_id[] = {
- { "m41t80", 0 },
- { "m41t81", M41T80_FEATURE_HT },
- { "m41t81s", M41T80_FEATURE_HT | M41T80_FEATURE_BL },
- { "m41t82", M41T80_FEATURE_HT | M41T80_FEATURE_BL },
- { "m41t83", M41T80_FEATURE_HT | M41T80_FEATURE_BL },
- { "m41st84", M41T80_FEATURE_HT | M41T80_FEATURE_BL },
- { "m41st85", M41T80_FEATURE_HT | M41T80_FEATURE_BL },
- { "m41st87", M41T80_FEATURE_HT | M41T80_FEATURE_BL },
+ { "m41t65", M41T80_FEATURE_HT | M41T80_FEATURE_WD },
+ { "m41t80", M41T80_FEATURE_SQ },
+ { "m41t81", M41T80_FEATURE_HT | M41T80_FEATURE_SQ},
+ { "m41t81s", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
+ { "m41t82", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
+ { "m41t83", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
+ { "m41st84", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
+ { "m41st85", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
+ { "m41st87", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
{ }
};
MODULE_DEVICE_TABLE(i2c, m41t80_id);
@@ -385,8 +388,12 @@ static ssize_t m41t80_sysfs_show_sqwfreq(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct i2c_client *client = to_i2c_client(dev);
+ struct m41t80_data *clientdata = i2c_get_clientdata(client);
int val;

+ if (!(clientdata->features & M41T80_FEATURE_SQ))
+ return -EINVAL;
+
val = i2c_smbus_read_byte_data(client, M41T80_REG_SQW);
if (val < 0)
return -EIO;
@@ -407,9 +414,13 @@ static ssize_t m41t80_sysfs_set_sqwfreq(struct device *dev,
const char *buf, size_t count)
{
struct i2c_client *client = to_i2c_client(dev);
+ struct m41t80_data *clientdata = i2c_get_clientdata(client);
int almon, sqw;
int val = simple_strtoul(buf, NULL, 0);

+ if (!(clientdata->features & M41T80_FEATURE_SQ))
+ return -EINVAL;
+
if (val) {
if (!is_power_of_2(val))
return -EINVAL;
@@ -498,6 +509,8 @@ static void wdt_ping(void)
.buf = i2c_data,
},
};
+ struct m41t80_data *clientdata = i2c_get_clientdata(save_client);
+
i2c_data[0] = 0x09; /* watchdog register */

if (wdt_margin > 31)
@@ -508,6 +521,12 @@ static void wdt_ping(void)
*/
i2c_data[1] = wdt_margin<<2 | 0x82;

+ /* M41T65 has three bits for resolution. Don't set bit 7, as that would
+ * be an invalid resolution.
+ */
+ if (clientdata->features & M41T80_FEATURE_WD)
+ i2c_data[1] &= ~0x80;
+
i2c_transfer(save_client->adapter, msgs1, 1);
}


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