From: Marek Vasut <marex@denx.de>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Robert Jarzmik <robert.jarzmik@free.fr>,
Brian Norris <computersforpeace@gmail.com>,
linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
Ezequiel Garcia <ezequiel.garcia@free-electrons.com>,
Scott Wood <scottwood@freescale.com>, Josh Wu <josh.wu@atmel.com>,
Kyungmin Park <kyungmin.park@samsung.com>,
Han Xu <han.xu@freescale.com>,
Huang Shijie <shijie.huang@arm.com>
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 [thread overview]
Message-ID: <201510291823.47976.marex@denx.de> (raw)
In-Reply-To: <20151029082448.2a89c791@bbrezillon>
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
next prev parent reply other threads:[~2015-10-29 17:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-27 2:31 [PATCH 0/5] mtd: migrate 'of_node' handling to core, not in mtd_part_parser_data Brian Norris
2015-10-27 2:31 ` [PATCH 1/5] mtd: ofpart: grab device tree node directly from master device node Brian Norris
2015-10-27 7:42 ` Boris Brezillon
2015-10-27 17:54 ` Brian Norris
2015-10-28 1:01 ` Brian Norris
2015-10-28 8:02 ` Boris Brezillon
2015-10-28 7:58 ` Boris Brezillon
2015-10-28 16:11 ` Marek Vasut
2015-10-28 16:32 ` Boris Brezillon
2015-10-28 17:14 ` Brian Norris
2015-10-28 20:55 ` Robert Jarzmik
2015-10-28 22:47 ` Marek Vasut
2015-10-29 6:32 ` Robert Jarzmik
2015-10-29 7:24 ` Boris Brezillon
2015-10-29 17:23 ` Marek Vasut [this message]
2015-10-29 17:34 ` Boris Brezillon
2015-10-29 20:28 ` Robert Jarzmik
2015-10-28 20:38 ` Marek Vasut
2015-10-27 2:31 ` [PATCH 2/5] mtd: nand: drop unnecessary partition parser data Brian Norris
2015-10-27 7:52 ` Boris Brezillon
2015-10-28 0:45 ` Brian Norris
2015-10-27 2:31 ` [PATCH 3/5] mtd: spi-nor: " Brian Norris
2015-10-27 2:31 ` [PATCH 4/5] mtd: " Brian Norris
2015-10-27 2:31 ` [PATCH 5/5] mtd: drop 'of_node' " Brian Norris
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