RE: [PATCH 0/9] drivers:mtd:UBI: add bakvol module for MLC NAND paired page issue

[Bean Huo éææ (beanhuo)]

> Hi Bean,
> 
> Next time you send a patch series, could send all the patches in reply to the
> cover letter?

No problem, we will format our submit-patch method, and standard it.


> > Hello,
> >
> > This series aims at adding a bakvol module for MLC NAND paired page
> > Power loss protection.
> > MLC NAND paired page power loss is a known issue so far, MLC NAND
> > pages are coupled in a sense that if you cut power while writing to a
> > page, you corrupt not only this page, but also one of the previous pages
> which is paired with the current one.
> > Currently, there is no a perfect solution for this.
> > This paired page solution is based on NAND multiple plane program
> > feature. For this Patch, only used dual plane page program, means two
> > different plane pages can Be programmed together at the same time.
> > Dual plane page program only implements in backup operation. Only
> > lower page data Be duplicated and back up into a internal log volume by
> dual plane program method.
> 
> Hm, I'm not very fond of the idea, especially because of the complexity caused
> by dual plane program operations (you can't take a random block to write your
> backup on it, which means WL is complexified too), and the fact that you're
> duplicating data (thus introducing a performance penalty and storage
> overhead).
Yes, dual plane program operation has special pages requirement. 
The page address bits, PA[7:0], must be identical for each issued address.
This is being defined by ONFI specification. It will definitely result in storage 
overhead, but the performance of dual plane program is better than normal page program.
Because we don't program source data and backup data one page by one page.

> >
> > This patch has been testing on Micron 70s/80s/90s MLC NAND.
> > Of course there are some places needed to be improved and simplified.
> >
> > Any suggestion and comments welcomed.
> 
> Sure, I'll try to review it soon.

Thanks, this is a initial version, I think, there are some places needed to be perfected.

> Thanks for submitting those patches.
> 
> Best Regards,
> 
> Boris
> 
> --
> Boris Brezillon, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com