Nand partitioning in u-boot

Question

I am working on an Embedded ARM9 development board. In that i want rearrange my nand partitions. Can anybody tell me how to do that ?

In my u-boot shell if i give the command mtdparts which gives following information .

Boardcon> mtdparts      

device nand0 <nandflash0>, # parts = 7

#: name                size            offset          mask_flags
0: bios                0x00040000      0x00000000      0
1: params              0x00020000      0x00040000      0
2: toc                 0x00020000      0x00060000      0
3: eboot               0x00080000      0x00080000      0
4: logo                0x00100000      0x00100000      0
5: kernel              0x00200000      0x00200000      0
6: root                0x03c00000      0x00400000      0

active partition: nand0,0 - (bios) 0x00040000 @ 0x00000000

defaults:
mtdids  : nand0=nandflash0 
mtdparts: mtdparts=nandflash0:256k@0(bios),128k(params),128k(toc),512k(eboot),1024k(logo),2m(kernel),-(root) 

Kernel boot message shows the following :

 Creating 3 MTD partitions on "NAND 64MiB 3,3V 8-bit":
 0x000000000000-0x000000040000 : "Boardcon_Board_uboot"
 0x000000200000-0x000000400000 : "Boardcon_Board_kernel"
 0x000000400000-0x000003ff8000 : "Boardcon_Board_yaffs2"

Anybody can please explain me what is the relation between both these messages . And which one either kernel or u-boot is responsible for creating partions on nand flash?. As for as i know kernel is not creating partitions on each boot but why the message "Creating 3 MTD partitions"?

Answer 1

For flash devices, either NAND or NOR, there is no partition table on the device itself. That is, you can't read the device in a flash reader and find some table that indicates how many partitions are on the device and where each partition begins and ends. There is only an undifferentiated sequence of blocks. This is a fundamental difference between MTD flash devices and devices such as disks or FTL devices such as MMC.

The partitioning of the flash device is therefore in the eyes of the beholder, that is, either U-Boot or the kernel, and the partitions are "created" when beholder runs. That's why you see the message Creating 3 MTD partitions. It reflects the fact that the flash partitions really only exist in the MTD system of the running kernel, not on the flash device itself.

This leads to a situation in which U-Boot and the kernel can have different definitions of the flash partitions, which is apparently what has happened in the case of the OP.

In U-Boot, you define the flash partitions in the mtdparts environment variable. In the Linux kernel, the flash partitions are defined in the following places:

1. In older kernels (e.g. 2.6.35 for i.MX28) the flash partitioning could be hard-coded in gpmi-nfc-mil.c or other driver source code. (what a bummer!).
2. In the newer mainline kernels with device tree support, you can define the MTD paritions in the device tree
3. In the newer kernels there is usually support for kernel command line partition definition using a command line like root=/dev/mmcblk0p2 rootwait console=ttyS2,115200 mtdparts=nand:6656k(all),1m(squash),-(jffs2)

The type of partitioning support that you have in the kernel therefore depends on the type of flash you are using, whether it's driver supports kernel command line parsing and whether your kernel has device tree support.

In any event, there is an inherent risk of conflict between the U-Boot and kernel partitioning of the flash. Therefore, my recommendation is to define the flash partitions in the U-Boot mtdparts variable and to pass this to the kernel in the U-Boot kernel command line, assuming that your kernel support this option.