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

[s-paulraj at ti.com]

From: Sandeep Paulraj <s-paulraj at ti.com>

This patch updates the README for NAND.
There were some good updates made to the driver.

Signed-off-by: Sandeep Paulraj <s-paulraj at ti.com>
---
 doc/README.nand |   42 ++++++++++++++++++++++++++++++++++++++++--
 1 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/doc/README.nand b/doc/README.nand
index 8eedb6c..57da255 100644
--- a/doc/README.nand
+++ b/doc/README.nand
@@ -147,6 +147,44 @@ NAND locking command (for chips with active LOCKPRE pin)
   "nand unlock [offset] [size]"
   unlock consecutive area (can be called multiple times for different areas)
 
+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.
+
+What is lacking?
+================
+
+We need to add 64 bit support in cmd_nand.c and env_nand.c as well.
+Without this certain diagnostcis 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.
+At this point of time it appears as if the entire common folder
+needs to be updated with 64 bit values.
+
+
+
 
-I have tested the code with board containing 128MiB NAND large page chips
-and 32MiB small page chips.
-- 
1.6.0.4