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SubjectRe: [PATCH] rtc: ds1307: Fix relying on reset value for weekday
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On Wednesday 01 June 2016 05:48 PM, Alexandre Belloni wrote:
> Hi,
>
> On 01/06/2016 at 16:19:07 +0530, Keerthy wrote :
>> The reset value of weekday is 0x1. This is wrong since
>> the reset values of the day/month/year make up to Jan 1 2001.
>> When computed weekday comes out to be Monday. On a scale
>> of 1-7(Sunday - Saturday) it should be 0x2. So we should not
>> be relying on the reset value.
>>
>
> Hum, what are the chances that the reset value is actually the correct
> date/time?
> Won't that be corrected after the first call to set_time? Until then,
> the date is not correct so, do we care anyway?

Yes if an alarm is programmed without set_time.

ex: rtcwake -d /dev/rtc0 -s 5

Even the basic rtctest under tools/testing/selftests/timers/rtctest.c fails
as the wday is wrong and no alarm fires.

Instead of relying on some one to call set_time before programming alarm
its better to fix the wday to reflect the current day right?


>
> Maybe I'm missing something here.
>
>> Hence compute the wday using the current date/month/year values.
>> Check if reset wday is any different from the computed wday,
>> If different then set the wday which we computed using
>> date/month/year values.
>>
>> Document Referred:
>> http://ww1.microchip.com/downloads/en/DeviceDoc/20002266F.pdf
>>
>> Fixes: 1d1945d261a2af "drivers/rtc/rtc-ds1307.c: add alarm support for mcp7941x chips"
>> Signed-off-by: Keerthy <j-keerthy@ti.com>
>> ---
>> drivers/rtc/rtc-ds1307.c | 28 +++++++++++++++++++++++++++-
>> 1 file changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
>> index 821d9c0..d9045cc 100644
>> --- a/drivers/rtc/rtc-ds1307.c
>> +++ b/drivers/rtc/rtc-ds1307.c
>> @@ -602,6 +602,8 @@ static const struct rtc_class_ops ds13xx_rtc_ops = {
>> * Alarm support for mcp794xx devices.
>> */
>>
>> +#define MCP794XX_REG_WEEKDAY 0x3
>> +#define MCP794XX_REG_WEEKDAY_WDAY_MASK 0x7
>> #define MCP794XX_REG_CONTROL 0x07
>> # define MCP794XX_BIT_ALM0_EN 0x10
>> # define MCP794XX_BIT_ALM1_EN 0x20
>> @@ -1231,13 +1233,16 @@ static int ds1307_probe(struct i2c_client *client,
>> {
>> struct ds1307 *ds1307;
>> int err = -ENODEV;
>> - int tmp;
>> + int tmp, wday;
>> struct chip_desc *chip = &chips[id->driver_data];
>> struct i2c_adapter *adapter = to_i2c_adapter(client->dev.parent);
>> bool want_irq = false;
>> bool ds1307_can_wakeup_device = false;
>> unsigned char *buf;
>> struct ds1307_platform_data *pdata = dev_get_platdata(&client->dev);
>> + struct rtc_time tm;
>> + unsigned long timestamp;
>> +
>> irq_handler_t irq_handler = ds1307_irq;
>>
>> static const int bbsqi_bitpos[] = {
>> @@ -1526,6 +1531,27 @@ read_rtc:
>> bin2bcd(tmp));
>> }
>>
>> + /*
>> + * Some IPs have weekday reset value = 0x1 which might not correct
>> + * hence compute the wday using the current date/month/year values
>> + */
>> + ds1307_get_time(&client->dev, &tm);
>> + wday = tm.tm_wday;
>> + timestamp = rtc_tm_to_time64(&tm);
>> + rtc_time64_to_tm(timestamp, &tm);
>> +
>> + /*
>> + * Check if reset wday is different from the computed wday
>> + * If different then set the wday which we computed using
>> + * timestamp
>> + */
>> + if (wday != tm.tm_wday) {
>> + wday = i2c_smbus_read_byte_data(client, MCP794XX_REG_WEEKDAY);
>> + wday = wday & ~MCP794XX_REG_WEEKDAY_WDAY_MASK;
>> + wday = wday | (tm.tm_wday + 1);
>> + i2c_smbus_write_byte_data(client, MCP794XX_REG_WEEKDAY, wday);
>> + }
>> +
>> if (want_irq) {
>> device_set_wakeup_capable(&client->dev, true);
>> set_bit(HAS_ALARM, &ds1307->flags);
>> --
>> 1.9.1
>

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