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SubjectRe: [v2] rtc: pcf85363/pcf85263: fix error that failed to run hwclock -w
On 16/08/2019 10:50:49-0500, Li Yang wrote:
> On Fri, Aug 16, 2019 at 3:05 AM Alexandre Belloni
> <alexandre.belloni@bootlin.com> 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.
>

Most of the i2c RTCs do address wrapping which is sometimes the only way
to properly set the time.


--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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