UBI: ignore/overwrite old data/PEBs after flashing

[Artem Bityutskiy]

On Thu, 2014-10-16 at 12:29 +0200, Rafał Miłecki wrote:
> On 16 October 2014 12:09, Artem Bityutskiy <dedekind1 at gmail.com> wrote:
> > On Thu, 2014-10-16 at 07:34 +0200, Rafał Miłecki wrote:
> >> Hi,
> >>
> >> I need some help with flashing UBI images.
> >>
> >> I work with Broadcom ARM SoCs that use a CFE bootloader. In most cases
> >> it doesn't provide a way to clear flash content before flashing the
> >> firmware. It means that if I have 120 MiB of space for the firmware
> >> and I flash 20 MiB firmware, the rest of flash (100 MiB) won't be
> >> cleared. My partitioner driver will create 2 MiB partition for kernel
> >> and 118 MiB partition for UBI.
> >
> > So what I hear is that the flasher does not provide users the "erase"
> > operation, but only provides users a "write" operation?
> 
> That's right (at least for some/most of the CFE versions). Some
> vendors hack CFE on their own, but the main problem still affects many
> devices.
> 
> 
> > Then the solution would be to pad your image with 0xFFs and write it.
> > UBI will notice PEBs which do not contain UBI headers and will erase
> > them in background.
> 
> That would be trivial trick to implement, however it's far from being
> user friendly. Most devices have 128 MiB flash and our firmware
> (OpenWrt) is only ~4 MiB big. It would be a waste of
> space/bandwidth/time to provide firmware images padded with over 120
> MiB of 0xFF.

Right, this is a work-around, and it is OK for a work-around to be
suboptimal, generally speaking.

If you want a more optimal work-around, it will be more intrusive. One
idea would be to can create a small specialized kernel driver which will
start before UBI and clean-up your flash: erase PEBs you specify it.
Something like 'mtd/flashcleaner.ko'.

May be you can invent an nice UBI feature to do this, but so far I feel
like a separate driver should be a better way to go.