Re: [PATCH v4 0/2] mtd: spi: nor: force mtd name to "nor%d"

[Tom Rini <trini@konsulko.com>]

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On Wed, Sep 22, 2021 at 08:24:18PM +0200, Marek Vasut wrote:
> On 9/22/21 7:29 PM, Marek Behún wrote:
> > (Adding also Tom.)
> > 
> > Hi Patrick, Marek,
> > 
> > I find this either not complete or not needed:
> > 
> > - either you need mtd names to be of this format so that old MTDPARTS
> >    config definitions do not need to be changed, i.e. something like
> >      CONFIG_MTDPARTS_DEFAULT="nor0:1M(u-boot),0x1000@0xfff000(env)"
> >    does not work currently, and you want to make it work.
> > 
> >    I find your solution here incomplete because MTDPARTS can also be
> >    used to be passed to Linux as mtdparts parameter, but there is no
> >    guarantee that the "norN" numbering you are creating in U-Boot will
> >    be the same as the one in kernel.
> > 
> > - or it is not needed, because you can remove MTDPARTS definition from
> >    the board config entirely and move the information into device tree.
> >    In fact this was the main idea behind making the series
> >      Support SPI NORs and OF partitions in `mtd list`
> >    The SPI-NOR MTDs after this series can have conflicting names,
> >    because you can still choose between them via OF path with the `mtd`
> >    command.
> > 
> >    Tom and I were of the opinion that MTDPARTS should be deprecated and
> >    removed in favor of OF. Marek Vasut says that this is not possible
> >    for every board, and so needs to stay.
> > 
> > BTW, I find it a little weird for Marek to defend old API which should
> > be converted to DT, when in discussion about DM USB / Nokia N900
> > USB TTY console [1] he was defending the opinion that we should be
> > heading to DT in U-Boot.
> > 
> > [1]
> > https://patchwork.ozlabs.org/project/uboot/patch/20210618145724.2558-1-pali@kernel.org/
> 
> That USB discussion is completely unrelated to the problem here, the USB
> discussion is about internal (i.e. not user facing) conversion to DM/DT. The
> user-facing ABI does not change there. Also, that discussion was about
> patching USB stack to permit new non-DM/DT operation, not fixing existing
> one.
> 
> This problem here is user facing ABI, the mtdparts/mtdids. That user facing
> ABI got broken. Boards which do depend on it, even those currently in tree,
> are broken. Not all boards can update their environment, so some backward
> compatibility of the user facing ABI should be in place, even though it
> might not be to the degree Linux kernel does so. So far, it seems most of
> the U-Boot command line interface has managed to retain backward
> compatibility, I don't see why this here should be handled any differently.
> 
> Note that there are not just a few boards that are broken, but hundreds. I
> believe that itself justifies a fix, instead of just throwing all those
> hundreds of boards overboard.
> 
> u-boot$ git grep -l CONFIG_MTDIDS configs | wc -l
> 203
> 
> Hopefully that clarifies the difference.

It doesn't quite, sorry.  If you have "mtdparts=... mtdids=..." in your
cmdline that you pass to Linux, U-Boot doesn't care.  That's one of the
main users of CONFIG_MTDIDS/MTDPARTS today, which could in some good
number of cases be removed (take am335x_evm_defconfig for example, the
table has been defined in the upstream DT for forever).  Taking a look
at:
commit 938db6fe5da3581ed2c17d64c7e016a7a8df5237
Author: Miquel Raynal <miquel.raynal@bootlin.com>
Date:   Sat Sep 29 12:58:30 2018 +0200

    cmd: mtdparts: describe as legacy
    
    The 'mtdparts' command is not needed anymore. While the environment
    variable is still valid (and useful, along with the 'mtdids' one), the
    command has been replaced by 'mtd' which is much more close to the MTD
    stack and do not add its own specific glue.
    
    Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
    Reviewed-by: Stefan Roese <sr@denx.de>
    Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>

Is when "mtdparts" in U-Boot was noted as legacy.  So what exactly are
we fixing with this series?  Nothing changed about hard-coded values
being passed along.  What may have broken was some progmatic way to set
those, but I think that's both fragile and deprecated in favor of the
table being in the DT.

-- 
Tom

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