mtd partitions limited to 4 GB?

[Josh Boyer]

On Mon, 16 Jun 2008 14:04:06 -1000
Mitch Bradley <wmb at firmworks.com> wrote:

> In drivers/mtd/mtdpart.c, struct mtd_part has  "u_int32_t offset", thus 
> (apparently) limiting the partition start offset to 4 GiB.  Similarly, 
> struct mtd_partition in include/linux/mtd/partititions.h has "u_int32_t 
> size" and "u_int32_offset".

This is not limited to partitions.  The entire MTD subsystem is limited
to 4 GiB sized devices.

> Now that NAND FLASH device sizes have exceeded that, this appears to be 
> a significant limitation.
> 
> Is anyone in the mtd community already addressing this?

There have been some that have offered to help in recent weeks.  A
brainstorming session of sorts happened on the list a couple of weeks
ago.  You might check there for what was decided.

> Fixing the core infrastructure might be as simple as using "loff_t" 
> instead of "u_int32_t" for those fields.  However, all of the existing 
> partition map parsers appear to have the same 32-bit limitation, so 
> partitioning a >4GiB device will require a new or modified partition map 
> format.

IIRC, one of the outcomes of the discussion was to introduce a new
interface so that chips are addressed in block+offset mappings.  This
will be better overall, but requires a bit more overhead in the initial
implementation.

josh