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Date:   Tue, 19 May 2020 11:08:40 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Bean Huo <huobean@gmail.com>
Cc:     richard@nod.at, vigneshr@ti.com, s.hauer@pengutronix.de,
        boris.brezillon@collabora.com, derosier@gmail.com,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
        Bean Huo <beanhuo@micron.com>
Subject: Re: [PATCH v4 0/5] Micron SLC NAND filling block
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        <8de0911281b4c03671841027ec165422789b63f2.camel@gmail.com>
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Hi Bean,

Bean Huo <huobean@gmail.com> wrote on Tue, 19 May 2020 11:04:15 +0200:

> hi,  Miquel
> 
> On Mon, 2020-05-18 at 17:22 +0200, Miquel Raynal wrote:
> > Hi Bean,
> > 
> > Bean Huo <huobean@gmail.com> wrote on Mon, 18 May 2020 15:59:38
> > +0200:
> >   
> > > From: Bean Huo <beanhuo@micron.com>
> > > 
> > > After submission of patch V1 [1] and V2 [2], we stopped its update
> > > since we get
> > > stuck in the solution on how to avoid the power-loss issue in case
> > > power-cut
> > > hits the block filling. In the v1 and v2, to avoid this issue, we
> > > always damaged
> > > page0, page1, this's based on the hypothesis that NAND FS is UBIFS.
> > > This
> > > FS-specifical code is unacceptable in the MTD layer. Also, it
> > > cannot cover all
> > > NAND based file system. Based on the current discussion, seems that
> > > re-write all
> > > first 15 page from page0 is a satisfactory solution.  
> > 
> > We have a layering problem now. Maybe we should just have an MTD
> > internal variable like min_written_pages_before_erase that the Micron
> > driver could set to a !0 value.
> > 
> > Then, the handling could be done by the user (UBI/UBIFS, JFFS2, MTD
> > user if exported).
> >   
> 
> This is NAND its own problem, if no significant adantage, I don't think
> it's a good solution to extend the problem to the upper FS layer.
> also, in the FS erase path, doesn't have the programmed pages counter.
> we should repeat the same approach as we did in MTD layer.

The problem is that if the filesystem is not aware, it breaks the
"power cut safe" assertion.

There is a problem with JFFS2 and a problem with UBIFS because of that.
We can certainly keep a default implementation like this one for other
users though.

> 
> > > 
> > > Meanwhile, I borrowed one idea from Miquel Raynal patchset [3], in
> > > which keeps
> > > a recode of programmed pages, base on it, for most of the cases, we
> > > don't need
> > > to read every page to see if current erasing block is a partially
> > > programmed
> > > block.
> > > 
> > > Changelog:
> > > 
> > > v3 - v4:
> > >     1. In the patch 4/5, change to directly use ecc.strength to
> > > judge the page
> > >        is a empty page or not, rather than max_bitflips < mtd-  
> > > >bitflip_threshold  
> > >     2. In the patch 5/5, for the powerloss case, from the next time
> > > boot up,
> > >        lots of page will be programmed from >page15 address, if
> > > still using
> > >        first_p as GENMASK() bitmask starting position, writtenp
> > > will be always 0,
> > >        fix it by changing its bitmask starting at bit position 0.
> > > 
> > > v2 - v3:
> > >     1. Rebase patch to the latest MTD git tree
> > >     2. Add a record that keeps tracking the programmed pages in the
> > > first 16
> > >        pages
> > >     3. Change from program odd pages, damage page 0 and page 1, to
> > > program all
> > >        first 15 pages
> > >     4. Address issues which exist in the V2.
> > > 
> > > v1 - v2:
> > >     1. Rebased V1 to latest Linux kernel.
> > >     2. Add erase preparation function pointer in
> > > nand_manufacturer_ops.
> > > 
> > > 
> > > [1] https://www.spinics.net/lists/linux-mtd/msg04112.html
> > > [2] https://www.spinics.net/lists/linux-mtd/msg04450.html
> > > [3] https://www.spinics.net/lists/linux-mtd/msg13083.html
> > > 
> > > 
> > > Bean Huo (5):
> > >   mtd: rawnand: group all NAND specific ops into new nand_chip_ops
> > >   mtd: rawnand: Add {pre,post}_erase hooks in nand_chip_ops
> > >   mtd: rawnand: Add write_oob hook in nand_chip_ops
> > >   mtd: rawnand: Introduce a new function
> > > nand_check_is_erased_page()
> > >   mtd: rawnand: micron: Micron SLC NAND filling block  
> > 
> > When you take my patches in your series, especially when not touching
> > them at all, you should keep my Authorship and SoB first, then add
> > your
> > SoB.
> >   
> 
> sorry for my fault, I thought adding your Signed-off-by in 3/5 is
> suffient. you mean I should add your signed-off-by in 5/5 as well?
> I will do that in next version.

You should keep my Authorship and SoB for both patches + add your SoB
after mine.


Thanks,
Miquèl