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    SubjectRe: [patch 2.6.19-git] rts-rs5c372 updates: more chips, alarm, 12hr mode, etc
    From
    > On Sunday 10 December 2006 10:27 pm, Voipio Riku wrote:
    >> > Update the rtc-rs5c372 driver:
    >> > I suspect the
    >> > issue wasn't that "mode 1" didn't work on that board; the original
    >> > code to fetch the trim was broken. If "mode 1" really won't work,
    >> > that's almost certainly a bug in that board's I2C driver.

    >> It was not related to trim fetching. Yes, it very likely that the boards
    >> i2c controller (i2c-iop3xx) is has a bug, but I'm not competent enough
    >> to
    >> find out what it is actually sending out to the wire.

    > I'd expect that would be the controller _driver_ ... although it would
    > not surprise me to know there were also (unfixed) silicon bugs to cope
    > with, like version-specific differences. One hopes errata are published
    > for the chip you're using, and that they don't lie.

    from what I saw, the driver simply passes messages over to the i2c
    controller. It even specifically mentiones that it supports repeated start
    conditions, as needed for read method #1. Comparing to 80219 manual[1], I
    did not spot anything obviously wrong.

    > Have you asked around for anyone who may have insights about i2c-iop3xx
    > driver bugs? Maybe the driver maintainers, or arm-linux folk, or on
    > the i2c list.

    I was told to contact Dan Williams, I didn't get any response.

    >> With your patch, the rtc acts like the chip would completely ignore the
    >> "address" transfer, and starts reading from the last (default) register
    >> anyway. Thus all the regs look shifted by one in the driver.

    > That's quite strange. The docs on the RTC are quite clear about what's
    > supposed to happen with what I2C messages. And I'd expect them to be
    > right ... especially since they behaved for me, and the original author
    > of that code! That makes me suspect that your particular I2C controller
    > driver must not be issuing the protocol requests it should be, at least
    > on your hardware and revision.

    Well at least I'm happy that there is now someone more experienced working
    on this driver. When I tried to get it working I could not find anyone
    with another board to verify if the original and/or my patch works for
    them..

    >> > + /* this implements the first (most portable) reading method
    >> > + * specified in the datasheet.
    >> > */

    >> Why is this method considered more portable? Howabout making the read
    >> method a module parameter?

    > Of the three methods, #2 depends on messages that not all I2C masters
    > are necessarily going to be able to issue, and #3 assumes that there's
    > no other I2C master accessing that chip.

    Agreed, I wouldn't consider method #2 either.

    > Plus, if I understand things correctly, using mode #3 would break when
    > writing

    I should not. Writing isn't related to reading methods according the
    datasheet[2]. It provides one addressing method for writing, and writing
    works fine our Thecus/Allnet hardware.

    [1] http://www.intel.com/design/iio/manuals/274017.htm
    [2] http://www.ricoh.com/LSI/product_rtc/2wire/5c372/5c372a-e.pdf
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