Messages in this thread | | | From | Marek Vasut <> | Subject | Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node | Date | Thu, 29 Oct 2015 18:23:47 +0100 |
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On Thursday, October 29, 2015 at 08:24:48 AM, Boris Brezillon wrote: > Hi Robert,
Hi!
> On Thu, 29 Oct 2015 07:32:33 +0100 > > Robert Jarzmik <robert.jarzmik@free.fr> wrote: > > Marek Vasut <marex@denx.de> writes: > > >> Isn't there the case of a single NAND controller with 2 identical > > >> chips, each a 8 bit NAND chip, and the controller aggregating them to > > >> offer the OS a single 16-bit NAND chip ? > > Honestly, I don't know how this can possibly work, do you have a real > example of that use case. > > Here are a few reasons making it impossible: > > 1/ NAND are accessed using specific command sequences, and those > commands and addresses cycles are sent on through the data bus (AFAIR > only the lower 8bits of a 16bits bus are used for those > command/address cycles), so even if you connect the CLE/ALE/CS/RB pins > on both chips, the one connected on the MSB side of the data bus will > just receive garbage during the command/address sequences, and your > program/read operations won't work
Unless you duplicate the command to both MSB and LSB.
> 2/ NAND chips can have bad blocks, so even if you were able to address > 2 chips (which according to #1 is impossible), you might try to write > on a bad block on the chip connected on the MSB side of the data bus.
This one is a valid problem. The other valid issue here is where the command might fail on one chip and pass on the other.
> 3/ There probably are plenty of other reasons why this is not > possible ;-).
It's possible, implementable, but a really bad idea.
Best regards, Marek Vasut
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