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    SubjectRe: [PATCH] Add optional chip erase functionality to AT25 EEPROM driver.
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    On 12/08/2019 16:51, David Laight wrote:
    > From: Joe Burmeister
    >> Sent: 09 August 2019 13:54
    >>
    >> Many, though not all, AT25s have an instruction for chip erase.
    >> If there is one in the datasheet, it can be added to device tree.
    >> Erase can then be done in userspace via the sysfs API with a new
    >> "erase" device attribute. This matches the eeprom_93xx46 driver's
    >> "erase".
    > Is it actually worth doing though?
    >
    > I'm guessing that device erase can easily take over a minute.


    That must depend on the AT25. The one we're using (AT25F512A), as it's
    setup, it's fast enough. The datasheet states "The CHIP ERASE cycle time
    typically is 2 seconds.". I've not timed it's because as I said, seamed
    fast enough.


    If you can't erase it, then it's basically write once, or you expose it
    with spi_dev to Flashrom to erase it.


    > When I looked at 'device erase' on an EEPROM it took just as long
    > as erasing the sectors one at a time - but without the warm cosy
    > feeling that progress was being made.


    I didn't look at sector erase as I'm only interested in erasing it all
    and there was a command for it. I figured if someone wanted sector by
    sector they would implement it.



    > Not only that you can't really interrupt the erase, so either
    > the application has to sleep uninterruptibly for the duration
    > or you have to have some kind of 'device busy' response while
    > it is done asynchronously.


    That's true, but as I said, it's fast enough it's not an issue for us.

    > David
    >
    > -
    > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
    > Registration No: 1397386 (Wales)

    Regards,

    Joe

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