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Re: Writeable JFFS partition



David Woodhouse wrote:
> 
> justin.wojdacki@xxxxxxx.com said:
> >  From what I've observed, there's a dependency between the arenas
> > defined in drivers/block/blkmem.c and the map defined in drivers/mtd/
> > maps/____.c.
> 
> I know nothing of blkmem.c. What is it?
> 

blkmem.c may be a uClinux-only thing, I'm not sure. In the "Block
Devices" menu, there's an option "ROM disk memory block device
(blkmem)". If set, then arenas are laid out as "disks" in address
space, with device ids of the form /dev/rom%d. 

From what you have said, it sounds like there should be no interaction
between the Block Memory driver and the MTD interface. However, if I
don't have the block memory driver included in the kernel, I can never
successfully mount a root file partition. The kernel insists on
mounting a /dev/rom%d (/dev/rom4, in my case). If the block memory
driver is included, the kernel mounts /dev/rom4 fine, recognizing that
it's a JFFS2 partition, and forcing it to be read-only.

The relevant bits of dmesg:

...
physmap flash device: 200000 at 1fc00000
Physically mapped flash: Found 1 x16 devices at 0x0 in 16-bit mode
Found: ST M29W160DB
number of JEDEC chips: 1
0: offset=0x0,size=0x4000,blocks=1
1: offset=0x4000,size=0x2000,blocks=2
2: offset=0x8000,size=0x8000,blocks=1
3: offset=0x10000,size=0x10000,blocks=31
mtd: Giving out device 0 to Physically mapped flash
ad6489_mtd_init() called
ad6489_probe() called
AD6489 Residential Gateway flash probe(0x1fc00000,2097152,2): 200000
at 1fc00000
Analog Devices AD6489 Residential Gateway, Rev 2.0: Found 1 x16
devices at 0x0 in 16-bit mode
Found: ST M29W160DB
number of JEDEC chips: 1
0: offset=0x0,size=0x4000,blocks=1
1: offset=0x4000,size=0x2000,blocks=2
2: offset=0x8000,size=0x8000,blocks=1
3: offset=0x10000,size=0x10000,blocks=31
Creating 4 MTD partitions on "Analog Devices AD6489 Residential
Gateway, Rev 2.0":
0x00000000-0x00004000 : "Bootstrap 1"
mtd: Giving out device 1 to Bootstrap 1
0x00004000-0x00008000 : "Configuration"
mtd: Giving out device 2 to Configuration
0x00008000-0x00020000 : "Bootstrap 2"
mtd: Giving out device 3 to Bootstrap 2
0x00020000-0x00200000 : "Root"
mtd: Giving out device 4 to Root
VFS: Cannot open root device "mtdblock4" or 1f:04
blkdev_get returned -19
Please append a correct "root=" boot option
Kernel panic: VFS: Unable to mount root fs on 1f:04

-- 
-------------------------------------------------
Justin Wojdacki        
justin.wojdacki@xxxxxxx.com         (408) 350-5032
Communications Processors Group -- Analog Devices

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