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

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Date:   Thu, 29 Aug 2019 10:14:18 +0800
From:   Biwen Li <biwen.li@....com>
To:     a.zummo@...ertech.it, alexandre.belloni@...tlin.com,
        leoyang.li@....com, broonie@...nel.org, nandor.han@...sala.com
Cc:     linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Biwen Li <biwen.li@....com>
Subject: [v5] rtc: pcf85363/pcf85263: fix error that failed to run hwclock -w

Issue:
    - # hwclock -w
      hwclock: RTC_SET_TIME: Invalid argument

Why:
    - 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).

How:
    - 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@....com>
---
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;
 
-- 
2.17.1