rtc: ds1307: Add support for configuring external clock pin ...

The DS1307 has a square wave output pin, which can be used to output a
clock signal from the DS1307.  Additionally, the DS1308 supports
configuring this pin as an input from an external clock source to
which it should sync itself.

Add support with OF device tree properties to configure these
settings.  Supported features are using the clock pin as an output, an
input, the rate of the pin, and if it should be enabled on battery
backup power.

The driver does not check that the selected features are supported by
the clock chip being used.  It is the designer's responsibility to
create a valid device tree node; the bootloader does not attempt to be
a device tree validator.

Signed-off-by: Trent Piepho <tpiepho@kymetacorp.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

rtc: ds1307: Add ds1308 to driver's ID list ...

As far as the driver is concerned, it's the same as a 1338.  It's too
bad the i2c drivers can't make use of OF compatible properties with a
list of compatible devices.

Signed-off-by: Trent Piepho <tpiepho@kymetacorp.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ds1307: Configure ds1341 for lowest power mode ...

Empirical observations show that configuring INTCN=1, ECLK=0, EGFIL=0,
DOSF=1 on DS1341 put the chip in the mode where it draws the least
amount fo current.

Add code to configure DS1341 in such a way in case Barebox is the last
code that runs on the processor before being shut down.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ds1307: Fix a bug in probe() ...

Add missing "~" to bit clearing operation.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

rtc: ds1307: Fix a memory leak ...

Several failure paths would result in control being transfered to
'exit' label, so instead of just returning error codes in those cases
we also need to free the memory allocated for 'ds1307'

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

rtc: ds1307: Add code to support ds1337/1341 ...

Port DS1337 specific bits from corresponding Linux driver and add
small changes needed for DS1341.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

of: use 'const void *' for struct of_device_id.data ...

Since 2011 barebox' of_device_id struct uses unsigned long type for data field:

    struct of_device_id {
            char *compatible;
            unsigned long data;
    };

Almost always struct of_device_id.data field are used as pointer
and need 'unsigned long' casting.

E.g. see 'git grep -A 4 of_device_id drivers/' output:

    drivers/ata/sata-imx.c:static __maybe_unused struct of_device_id imx_sata_dt_ids[] = {
    drivers/ata/sata-imx.c- {
    drivers/ata/sata-imx.c-         .compatible = "fsl,imx6q-ahci",
    drivers/ata/sata-imx.c-         .data = (unsigned long)&data_imx6,
    drivers/ata/sata-imx.c- }, {

Here is of_device_id struct in linux kernel v4.0:

    struct of_device_id {
            char name[32];
            char type[32];
            char compatible[128];
            const void *data;
    };

Changing of_device_id.data type to 'const void *data' will increase
barebox' linux kernel compatibility and decrease number of 'unsigned
long' casts.

Part of the patch was done using the 'coccinelle' tool with the
following semantic patch:

    @rule1@
    identifier dev;
    identifier type;
    identifier func;
    @@
    func(...) {
    <...
    - dev_get_drvdata(dev, (unsigned long *)&type)
    + dev_get_drvdata(dev, (const void **)&type)
    ...>
    }
    @rule2@
    identifier dev;
    identifier type;
    identifier func;
    identifier data;
    @@
    func(...) {
    <...
    - dev_get_drvdata(dev, (unsigned long *)&type->data)
    + dev_get_drvdata(dev, (const void **)&type->data)
    ...>
    }

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

rtc: import ds1307 driver from linux-3.15 ...

Current ds1307 rtc driver supports only ds1307 and ds1338 chips;
it has no nvram support at the moment.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>