linux-kernel - Re: [PATCH] rtc: ds1307: Fix relying on reset value for weekday

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Date:	Tue, 7 Jun 2016 14:59:05 +0530
From:	Keerthy <a0393675@...com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Keerthy <j-keerthy@...com>
CC:	<a.zummo@...ertech.it>, <nm@...com>, <rtc-linux@...glegroups.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rtc: ds1307: Fix relying on reset value for weekday

Hi Alexandre,

On Wednesday 01 June 2016 06:06 PM, Keerthy wrote:
>
>
> 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.

Let me know if you feel this is a valid fix.

Regards,
Keerthy
>>
>>> 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@...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
>>