Hi,
On 01/08/2016 at 17:50:36 +0200, Martin Fuzzey wrote :
> The hardware has neither a century register nor a century warp around bit.
>
> However it does have a single byte of non volatile RAM.
>
> Use this to provide full century and wrap around support by storing:
> * The current century
> * The current half century (lower=00-49, upper=50-99)
>
> If the byte is not set the 21st century is assumed.
>
While the idea is certainly interesting and properly implemented, this
is not working as expected because the RTC thinks that year 00 is a leap
year and both 1900 and 2100 are not leap years.
While it is possible to wark around that, I don't think there is any
added benefit as this RTC will work properly as is until 2099 (and by
then it will probably have been replaced).
> Signed-off-by: Martin Fuzzey <mfuzzey@xxxxxxxxxxx>
> ---
> drivers/rtc/rtc-pcf85263.c | 105 +++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 103 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-pcf85263.c b/drivers/rtc/rtc-pcf85263.c
> index 997742d..7b55d92 100644
> --- a/drivers/rtc/rtc-pcf85263.c
> +++ b/drivers/rtc/rtc-pcf85263.c
> @@ -83,6 +83,10 @@
>
> #define PCF85263_HR_PM BIT(5)
>
> +/* Our data stored in the RAM byte */
> +#define PCF85263_STATE_CENTURY_MASK 0x7f
> +#define PCF85263_STATE_UPPER_HALF_CENTURY BIT(7)
> +
> enum pcf85263_irqpin {
> PCF85263_IRQPIN_NONE,
> PCF85263_IRQPIN_INTA,
> @@ -101,6 +105,8 @@ struct pcf85263 {
> struct regmap *regmap;
> enum pcf85263_irqpin irq_pin;
> int irq;
> + u8 century; /* 1 = 1900 2 = 2000, ... */
> + bool century_half; /* false = 0-49, true=50-99 */
> bool mode_12h;
> };
>
> @@ -136,6 +142,85 @@ static int pcf85263_bin24h_to_bcd12h(int hr24)
> return bin2bcd(hr12) | pm ? 0 : PCF85263_HR_PM;
> }
>
> +static inline bool pcf85263_century_half(int year)
> +{
> + return (year % 100) >= 50;
> +}
> +
> +/*
> + * Since the hardware only has a year range of 00 to 99 we use
> + * the ram byte to store the century. 1=1900, 2=2000, 3=2100
> + * A value of zero is assumed to be 2000
> + *
> + * Set the ram byte when we set the clock which lets us use any
> + * century supported by linux (tm_year=0 => 1900)
> + *
> + * Unfortunately the hardware has no wrap around flag so fix it
> + * by also storing a flag indicating if the year is in the
> + * upper or lower half of the century.
> + */
> +static int pcf85263_update_ram_byte(struct pcf85263 *pcf85263)
> +{
> + u8 val = pcf85263->century & PCF85263_STATE_CENTURY_MASK;
> +
> + if (pcf85263->century_half)
> + val |= PCF85263_STATE_UPPER_HALF_CENTURY;
> +
> + return regmap_write(pcf85263->regmap, PCF85263_REG_RAM_BYTE, val);
> +}
> +
> +static int pcf85263_read_ram_byte(struct pcf85263 *pcf85263)
> +{
> + unsigned int regval;
> + int ret;
> +
> + ret = regmap_read(pcf85263->regmap, PCF85263_REG_RAM_BYTE, ®val);
> + if (ret)
> + return ret;
> +
> + pcf85263->century = regval & PCF85263_STATE_CENTURY_MASK;
> + pcf85263->century_half = !!(regval & PCF85263_STATE_UPPER_HALF_CENTURY);
> +
> + if (!pcf85263->century) { /* Not valid => not initialised yet */
> + int year;
> +
> + ret = regmap_read(pcf85263->regmap,
> + PCF85263_REG_RTC_YR, ®val);
> + if (ret)
> + return ret;
> +
> + pcf85263->century = 2;
> + year = bcd2bin(regval) + 1900 + (pcf85263->century - 1) * 100;
> + pcf85263->century_half = pcf85263_century_half(year);
> +
> + dev_warn(pcf85263->dev, "No century in NVRAM - assume %d\n",
> + year);
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Detect year overflow by comparing the half (upper, lower) of
> + * the current year with the half the last time we read it
> + */
> +static int pcf85263_update_century(struct pcf85263 *pcf85263, int year)
> +{
> + bool cur_century_half;
> +
> + cur_century_half = pcf85263_century_half(year);
> +
> + if (cur_century_half == pcf85263->century_half)
> + return 0;
> +
> + if (!cur_century_half) /* Year has wrapped around */
> + pcf85263->century++;
> +
> + pcf85263->century_half = cur_century_half;
> +
> + return pcf85263_update_ram_byte(pcf85263);
> +}
> +
> static int pcf85263_read_time(struct device *dev, struct rtc_time *tm)
> {
> struct pcf85263 *pcf85263 = dev_get_drvdata(dev);
> @@ -169,7 +254,11 @@ static int pcf85263_read_time(struct device *dev, struct rtc_time *tm)
> tm->tm_mon = bcd2bin(regs[PCF85263_REG_RTC_MO - first]) - 1;
> tm->tm_year = bcd2bin(regs[PCF85263_REG_RTC_YR - first]);
>
> - tm->tm_year += 100; /* Assume 21st century */
> + ret = pcf85263_update_century(pcf85263, tm->tm_year);
> + if (ret)
> + return ret;
> +
> + tm->tm_year += (pcf85263->century - 1) * 100;
>
> return 0;
> }
> @@ -214,7 +303,14 @@ static int pcf85263_set_time(struct device *dev, struct rtc_time *tm)
> }
>
> /* Start it again */
> - return regmap_write(pcf85263->regmap, PCF85263_REG_STOPENABLE, 0);
> + ret = regmap_write(pcf85263->regmap, PCF85263_REG_STOPENABLE, 0);
> + if (ret)
> + return ret;
> +
> + pcf85263->century = (tm->tm_year / 100) + 1;
> + pcf85263->century_half = pcf85263_century_half(tm->tm_year);
> +
> + return pcf85263_update_ram_byte(pcf85263);
> }
>
> static int pcf85263_enable_alarm(struct pcf85263 *pcf85263, bool enable)
> @@ -422,6 +518,11 @@ static int pcf85263_init_hw(struct pcf85263 *pcf85263)
> return ret;
> }
>
> + /* Get our persistent state from the ram byte */
> + ret = pcf85263_read_ram_byte(pcf85263);
> + if (ret < 0)
> + return ret;
> +
> /* Determine 12/24H mode */
> ret = regmap_read(pcf85263->regmap, PCF85263_REG_OSC, ®val);
> if (ret)
>
--
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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