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Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node

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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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[PATCH 0/5] mtd: migrate 'of_node' handling to core, not in mtd_part_parser_data Brian Norris <computersforpeace@gmail.com> - 2015-10-27 03:40 +0100
  [PATCH 3/5] mtd: spi-nor: drop unnecessary partition parser data Brian Norris <computersforpeace@gmail.com> - 2015-10-27 03:40 +0100
  [PATCH 4/5] mtd: drop unnecessary partition parser data Brian Norris <computersforpeace@gmail.com> - 2015-10-27 03:40 +0100
  [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Brian Norris <computersforpeace@gmail.com> - 2015-10-27 03:40 +0100
    Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Boris Brezillon <boris.brezillon@free-electrons.com> - 2015-10-27 08:50 +0100
      Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Brian Norris <computersforpeace@gmail.com> - 2015-10-27 19:00 +0100
        Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Brian Norris <computersforpeace@gmail.com> - 2015-10-28 02:10 +0100
          Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Boris Brezillon <boris.brezillon@free-electrons.com> - 2015-10-28 09:10 +0100
        Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Boris Brezillon <boris.brezillon@free-electrons.com> - 2015-10-28 09:00 +0100
          Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Marek Vasut <marex@denx.de> - 2015-10-28 17:20 +0100
            Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Boris Brezillon <boris.brezillon@free-electrons.com> - 2015-10-28 17:40 +0100
              Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Brian Norris <computersforpeace@gmail.com> - 2015-10-28 18:20 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Robert Jarzmik <robert.jarzmik@free.fr> - 2015-10-28 22:10 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Marek Vasut <marex@denx.de> - 2015-10-28 23:50 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Robert Jarzmik <robert.jarzmik@free.fr> - 2015-10-29 07:40 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Boris Brezillon <boris.brezillon@free-electrons.com> - 2015-10-29 08:30 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Marek Vasut <marex@denx.de> - 2015-10-29 18:30 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from  master device node Boris Brezillon <boris.brezillon@free-electrons.com> - 2015-10-29 18:40 +0100
                Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Robert Jarzmik <robert.jarzmik@free.fr> - 2015-10-29 21:40 +0100
              Re: [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Marek Vasut <marex@denx.de> - 2015-10-28 21:40 +0100
  [PATCH 5/5] mtd: drop 'of_node' partition parser data Brian Norris <computersforpeace@gmail.com> - 2015-10-27 03:40 +0100

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