Re: [v2] rtc: pcf85363/pcf85263: fix error that failed to run hwclock -w

From: Li Yang
Date: Fri Aug 16 2019 - 11:51:04 EST


On Fri, Aug 16, 2019 at 3:05 AM Alexandre Belloni
<alexandre.belloni@xxxxxxxxxxx> wrote:
>
> On 16/08/2019 10:46:36+0800, Biwen Li wrote:
> > Issue:
> > - # hwclock -w
> > hwclock: RTC_SET_TIME: Invalid argument
> >
> > Why:
> > - Relative patch: https://lkml.org/lkml/2019/4/3/55 , this patch
> > will always check for unwritable registers, it will compare reg
> > with max_register in regmap_writeable.
> >
> > - In drivers/rtc/rtc-pcf85363.c, CTRL_STOP_EN is 0x2e, but DT_100THS
> > is 0, max_regiter is 0x2f, then reg will be equal to 0x30,
> > '0x30 < 0x2f' is false,so regmap_writeable will return false.
> >
> > - Root cause: the buf[] was written to a wrong place in the file
> > drivers/rtc/rtc-pcf85363.c
> >
>
> This is not true, the RTC wraps the register accesses properly and this

This performance hack probably deserve some explanation in the code comment. :)

> is probably something that should be handled by regmap_writable.

The address wrapping is specific to this RTC chip. Is it also
commonly used by other I2C devices? I'm not sure if regmap_writable
should handle the wrapping case if it is too special.

Regards,
Leo