[U-Boot] [PATCH] NAND: Updating the NAND README

[Scott Wood]

On Tue, Dec 01, 2009 at 01:06:07PM -0500, s-paulraj at ti.com wrote:
> +MTD NAND 64 bit support:
> +========================
> +
> +The MTD NAND infrastructure in U-Boot(until release 2009.11) used only
> +32 bit values to represent device size. As a result of which if we use
> +a NAND device of size 4 GB and above, the MTD NAND driver will not detect
> +such a NAND device due to overflow.
> +NANDs comes in various flavours. There are some NANDs which are
> +internally 2 devices and have 2 chipselects. If the SOC specific
> +NAND driver is designed to treat each NAND device as a separate device
> +then we will still be able to detect the entire 4GB of a NAND device.
> +Each chipselect being responsible for 2 GB address space.
> +But if at the U-Boot level we want to have access to the entire 4GB address
> +space then the only way to achieve this is to update the MTD and NAND drivers
> +with 64 bit values.
> +The Linux kernel was updated with 64 bit values sometime in December '08.
> +The core NAND driver is now similar to the core NAND driver in the kernel.
> +We appropriately update the MTD layer in U-Boot.
> +In the process of syncing up with the kernel we have also updated the
> +NAND driver with other enhancements that made its way to the NAND driver.
> +
> +After these features were added, testing was performed on a wide
> +range of NAND devices with page size of 64 KiB, 128KiB, 256KiB and 512
> +KiB. Also 2 separate 4GB NAND devices(one from SAMSUNG and one from MICRON)
> +were successfully tested. U-Boot was able to correctly detect the device
> +and read bad blocks.

Hmm, not sure we need to describe here what was, rather than what is.

> +What is lacking?
> +================
> +
> +We need to add 64 bit support in cmd_nand.c and env_nand.c as well.
> +Without this certain diagnostcis

typo

> will fail. For example,
> +issuing a "nand bad" command results in the same bad blocks being
> +found infinite times. This happens if we use a 4 GB NAND device.
> +This will not occur if NANDs of smalles than 4 GB are used.

s/of smalles than/smaller than/

> +At this point of time it appears as if the entire common folder
> +needs to be updated with 64 bit values.

Yeah...  If you want to put a concise note about this here, I'll add it,
though an actual bug tracking system would be nice. :-)

-Scott