Date:	Wed, 6 Jan 2016 15:29:22 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	潘栋 <peterpansjtu@...il.com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Pan <peterpandong@...ron.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
	karlzhang@...ron.com, Frans Klaver <fransklaver@...il.com>,
	David Woodhouse <dwmw2@...radead.org>, beanhuo@...ron.com
Subject: Re: [PATCH v2 00/12] mtd: nand_bbt: introduce independent nand BBT

On Wed, 30 Dec 2015 09:31:06 +0100
Boris Brezillon <boris.brezillon@...e-electrons.com> wrote:

> Hi Peter,
> 
> On Wed, 30 Dec 2015 15:18:39 +0800
> 潘栋 <peterpansjtu@...il.com> wrote:
> 
> > Hi Boris and Ezequiel,
> > 
> > 2015-12-29 23:11 GMT+08:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> > > On Tue, 29 Dec 2015 12:07:50 -0300
> > > Ezequiel Garcia <ezequiel@...guardiasur.com.ar> wrote:
> > >
> > >> On 29 December 2015 at 06:35, Boris Brezillon
> > >> <boris.brezillon@...e-electrons.com> wrote:
> > >> > Hi,
> > >> >
> > >> > On Mon, 28 Dec 2015 17:42:50 -0300
> > >> > Ezequiel Garcia <ezequiel@...guardiasur.com.ar> wrote:
> > >> >
> > >> >> This is looking a lot better, thanks for the good work!
> > >> >>
> > >> >> On 15 December 2015 at 02:59, Peter Pan <peterpansjtu@...il.com> wrote:
> > >> >> > Currently nand_bbt.c is tied with struct nand_chip, and it makes other
> > >> >> > NAND family chips hard to use nand_bbt.c. Maybe it's the reason why
> > >> >> > onenand has own bbt(onenand_bbt.c).
> > >> >> >
> > >> >> > Separate struct nand_chip from BBT code can make current BBT shareable.
> > >> >> > We create struct nand_bbt to take place of nand_chip in nand_bbt.c.
> > >> >> > Struct nand_bbt contains all the information BBT needed from outside and
> > >> >> > it should be embedded into NAND family chip struct (such as struct nand_chip).
> > >> >> > NAND family driver should allocate, initialize and free struct nand_bbt.
> > >> >> >
> > >> >> > Below is mtd folder structure we want:
> > >> >> >         mtd
> > >> >> >         ├── Kconfig
> > >> >> >         ├── Makefile
> > >> >> >         ├── ...
> > >> >> >         ├── nand_bbt.c
> > >> >>
> > >> >> Hm.. I'm not sure about having nand_bbt.c in drivers/mtd.
> > >> >> What's wrong with drivers/mtd/nand ?
> > >> >
> > >> > I haven't reviewed the series yet, but I agree. If the BBT code is only
> > >> > meant to be used on NAND based devices, it should probably stay in
> > >> > drivers/mtd/nand.
> > >> >
> > >> >>
> > >> >> In fact, I  was thinking we could go further and clean up the directories a bit
> > >> >> by separating core code, from controllers code, from SPI NAND code:
> > >> >>
> > >> >> drivers/mtd/nand/
> > >> >> drivers/mtd/nand/controllers
> > >> >> drivers/mtd/nand/spi
> > >> >>
> > >> >> Makes any sense?
> > >> >
> > >> > Actually I had the secret plan of moving all (raw) NAND controller
> > >> > drivers into the drivers/mtd/nand/controllers directory, though this
> > >> > was for a different reason: I'd like to create another directory for
> > >> > manufacturer specific code in order to support some advanced features
> > >> > on NANDs that do not implement (or only partially implement) the ONFI
> > >> > standard.
> > >> >
> > >> > The separation you're talking about here is more related to the
> > >> > interface used to communicate with the NAND chip.
> > >> >
> > >> > How about using the following hierarchy?
> > >> >
> > >> > drivers/mtd/nand/<nand-core-code>
> > >> > drivers/mtd/nand/interfaces/raw/<raw-nand-core-code>
> > >> > drivers/mtd/nand/interfaces/raw/controllers/<raw-nand-controller-drivers>
> > >> > drivers/mtd/nand/interfaces/spi/<spi-nand-code>
> > >> > drivers/mtd/nand/interfaces/onenand/<onenand-code>
> > >> > drivers/mtd/nand/chips/<manufacturer-spcific-code>
> > >> >
> > >> > What do you think?
> > >> >
> > >>
> > >> I believe we are bikeshedding here, but what the heck.
> > >>
> > >> That seems too involved. A simpler hierarchy could be clear enough,
> > >> and seems to follow what other subsystems do:
> > >>
> > >> drivers/mtd/nand/<all-nand-core-code>
> > >> drivers/mtd/nand/raw/<raw-nand-controller-drivers>
> > >
> > > And probably some common logic in there too.
> > >
> > >> drivers/mtd/nand/spi/<spi-nand-code>
> > >> drivers/mtd/nand/onenand/<onenand-code>
> > >> drivers/mtd/nand/chips/<manufacturer-spcific-code>
> > >>
> > >
> > > I'm fine with this one too ;-).
> > 
> > I'm fine with this structure too. drivers/mtd/nand folder becomes top folder for
> > all NAND based devices. Because (raw)NAND, SPI-NAND and ONENAND have
> > different command set and feature, each has its own core - nand_base.c
> > spi-nand-base.c
> > and onenand_base.c. So maybe it'll take a lot effort to abstract a
> > all-nand-core-code
> > (of course BBT should be one of them). What's your opinion?
> 
> Absolutely, that was the idea: move everything into the
> drivers/mtd/nand directory (with the structure described above), keep
> some specific logic for each interface type, and see if we can factor
> out some common code (I noticed that SPI NAND devices have a parameter
> page which looks similar to the one exposed by ONFI compliant devices,
> except this parameter page is retrieved using a different command, the
> same goes for the ->{set,get}_features() functions).
> But let's focus on the nand_bbt code for now.
> 
> > 
> > Also, please review the BBT patch if you have time. I think it's
> > helpful on the new NAND code
> > hierarchy.
> 
> I'll try to review it this week.

I'm a bit late, but I think I've reviewed most of it now.


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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