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    SubjectRe: RTC: add RTC class interface to m41t00 driver
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    On Sat, 5 Aug 2006 12:13:49 -0700, David Brownell <david-b@pacbell.net> wrote:
    > > 1. The driver contains ds_1340 (or st m41t00) definition, but it seems
    > > no way to select the ds_type.
    >
    > Which is harmless, since the driver has no code that really needs to care.
    > As I said, it's a least-common-denominator driver ... used in my case
    > with a SOC that integrates a highly functional (primary) RTC, because
    > only the external RTC provides its own battery-backed power domain.

    Oh, I missed that point. It should work for m41t00 indeed.

    > This is a limitation of the I2C stack ... one that I observe is being
    > worked around by m41t00.c platform_device tricks. A side effect of those
    > tricks is to prevent hooking up more than one of this type I2C chip
    > to a system ... not pretty (especially given that it's not documented),
    > but often OK.

    Yes, some more works would be needed on m41t00 to support multiple
    (different) M41Txx chips at same time.

    > It would have made more sense to me to have the M41T81 and M41T85 be
    > in a different driver, because of the incompatible register layout.
    > That's the more traditional approach.

    Now I'm thinking this way. Still thinking...

    > My approach was to go for "least common denominator", not "super generic".
    > Also, I avoided trying to work around I2C stack issues like the omission
    > of per-board tables/customization. When I2C eventually has a nice clean
    > solution for those issues, I expect that will mean adopting the better
    > solution involves fewer changes.

    OK, I see. I think LCD approach is worth indeed.

    > But I was mostly pointing out that if the goal was to support the m41t00
    > RTC (the normal reading of $SUBJECT), that work has been done for some
    > time and has already been pushed upstream.

    My real target is M41T80, which seems a subset of M41T81.
    (Sorry for not writing this before.)

    I agree m41t00 can be supported by rtc-ds1307 driver already.

    So the next theme would be how we support M41T8x chips. I think
    Alexander's rtc-m41txx is good candidate for them.

    Then M41T00 users can choose rtc-ds1307 or rtc-m41t00. Not so bad, I
    think.

    ---
    Atsushi Nemoto
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