RFC: detect and manage power cut on MLC NAND

[Artem Bityutskiy]

On Tue, 2015-03-10 at 12:57 +0100, Andrea Scian wrote:
> Dear All,
> 
> for testing and research purpose, I'm working with an Embedded Linux
> product which mounts an MLC NAND.
> 
> I know that one of the trouble with MLC flash on Linux with UBI/UBIFS is
> the power cut management (ref.
> http://www.linux-mtd.infradead.org/doc/ubifs.html#L_unstable_bits)
> 
> IIUC the solution inside MTD/UBI/UBIFS is not so simple and thus not so
> quick to implement.
> 
> I'm wondering if anyone of you already think about managing power cut in
> a different way: many embedded/industrial products already have some
> big/huge bypass capacitor that are able to keep the system alive for
> hundreds of milliseconds (this is useful for power supply
> micro-interruptions), which are commonly enough to complete the latest
> NAND operation.
> Most of the has a GPIO/IRQ that tells whenever such a power cut happens,
> so the kernel can take some actions with it (e.g., in our case, complete
> the last NAND operation and prevent from starting newer operation, which
> may corrupt the NAND pages).
> 
> WDYT about this?
> If it sounds reasonable is there any suggestion where to place such a code?

Ccing Boris, he has been looking into this area lately.

Artem.