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Date: Tue, 10 Mar 2015 13:51:15 +0100
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Subject: Re: RFC: detect and manage power cut on MLC NAND
From: Richard Weinberger <richard.weinberger@gmail.com>
To: Andrea Scian <rnd4@dave-tech.it>
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On Tue, Mar 10, 2015 at 12:57 PM, Andrea Scian <rnd4@dave-tech.it> 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?

Customers often use DYI uninterruptible power supplies using capacitors.
But managing a power cut is the least problem you have with MLC NAND.

-- 
Thanks,
//richard