Re: [RFC PATCH] mtd: rawnand: Remove docg4

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Boris,

Boris Brezillon <boris.brezillon@bootlin.com> wrote on Mon, 30 Jul 2018
22:13:41 +0200:

> The diskonchip G4 driver does not fit very well in the raw/parallel
> NAND framework simply because such chips have an internal controller
> translating DoC-specific commands into NAND ones.
> 
> Keeping such a driver in the raw NAND framework is a real burden for
> NAND maintainers.
> 
> Not to mention that some part in this drivers are a bit worrisome:
> 
> - writes are done by subpages, even though we're interfacing with an MLC
>   chip which are known to not support subpage writes very well (it might
>   be that the FTL handles the complexity for us though)
> 
> - some part of the code are simply ignoring return codes of function that
>   can fail in a few occasions
> 
> - there's a hack to support OOB writes when no data is provided. This
>   operation is not supported by the chip and should have been rejected,
>   and nandwrite and other userspace tools should have been patched to
>   deal with such devices
> 
> - the driver is apparently broken when ignore_badblocks module param
>   is not set to 1 and nobody noticed that (don't know since when this
>   is the case, but it's not a recent change)
>   http://lists.infradead.org/pipermail/linux-mtd/2018-July/082472.html
> 
> Add to that the fact that we already have a docg3 driver in
> drivers/mtd/devices/docg3.c and, looking at the code (and regs), it
> seems docg3 and docg4 have a lot in common (even the author of this
> driver seemed to have realized that interfacing with the raw NAND
> framework might have been a bad idea
> http://lists.infradead.org/pipermail/linux-mtd/2012-January/039517.html).
> 
> For all these reasons, I'm proposing to remove this driver. If anyone
> ever wants to add support for this chip back, I'd suggest extending
> the docg3 driver instead of adding a completely new driver.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> Cc: Mike Dunn <mikedunn@newsguy.com>
> Cc: Robert Jarzmik <robert.jarzmik@free.fr>
> Cc: Sergey Larin <cerg2010cerg2010@mail.ru>
> ---

I do agree in removing this driver.

I just checked for docg4 references and it looks like palmeo.c board
file has some code related to it, enclosed in a

        #if IS_ENABLED(CONFIG_MTD_NAND_DOCG4)

Besides the fact that it is the only user, that's probably something
we should also remove.

Plus, I recently added a mention to the docg4 driver in nand_base.c
during the conversion to nand_scan() (to skip nand_scan_ident()). It
might be worth removing the extra code or at least the reference in the
comment.

Thanks,
Miquèl