[v5] rtc: pcf85363/pcf85263: fix error that failed to run hwclock -w

From: Biwen Li
Date: Wed Aug 28 2019 - 22:24:27 EST

- # hwclock -w
hwclock: RTC_SET_TIME: Invalid argument

- Relative commit: 8b9f9d4dc511309918c4f6793bae7387c0c638af, this patch
will always check for unwritable registers, it will compare reg
with max_register in regmap_writeable.

- The pcf85363/pcf85263 has the capability of address wrapping
which means if you access an address outside the allowed range
(0x00-0x2f) hardware actually wraps the access to a lower address.
The rtc-pcf85363 driver will use this feature to configure the time
and execute 2 actions in the same i2c write operation (stopping the
clock and configure the time). However the driver has also
configured the `regmap maxregister` protection mechanism that will
block accessing addresses outside valid range (0x00-0x2f).

- Split of writing regs to two parts, first part writes control
registers about stop_enable and resets, second part writes
RTC time and date registers.

Signed-off-by: Biwen Li <biwen.li@xxxxxxx>
Change in v5:
- drop robust explanation

Change in v4:
- use old scheme
- replace link to lkml.org with commit
- add proper explanation

Change in v3:
- replace old scheme with new scheme:
increase max_register.

Change in v2:
- add Why and How into commit message.

drivers/rtc/rtc-pcf85363.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-pcf85363.c b/drivers/rtc/rtc-pcf85363.c
index a075e77617dc..3450d615974d 100644
--- a/drivers/rtc/rtc-pcf85363.c
+++ b/drivers/rtc/rtc-pcf85363.c
@@ -166,7 +166,12 @@ static int pcf85363_rtc_set_time(struct device *dev, struct rtc_time *tm)
buf[DT_YEARS] = bin2bcd(tm->tm_year % 100);

ret = regmap_bulk_write(pcf85363->regmap, CTRL_STOP_EN,
- tmp, sizeof(tmp));
+ tmp, 2);
+ if (ret)
+ return ret;
+ ret = regmap_bulk_write(pcf85363->regmap, DT_100THS,
+ buf, sizeof(tmp) - 2);
if (ret)
return ret;