[U-Boot] [PATCH] cmd: mtdparts: Probe MTD devices in mtdparts_init()

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

Hi Boris,

Boris Brezillon <boris.brezillon@bootlin.com> wrote on Tue, 30 Oct 2018
23:02:50 +0100:

> On Tue, 30 Oct 2018 11:59:13 +0100
> Stefan Roese <sr@denx.de> wrote:
> 
> > On 30.10.18 11:41, Boris Brezillon wrote:  
> > > On Tue, 30 Oct 2018 11:13:37 +0100
> > > Stefan Roese <sr@denx.de> wrote:
> > >     
> > >> Hi Boris,
> > >>
> > >> On 30.10.18 11:03, Boris Brezillon wrote:    
> > >>> On Tue, 30 Oct 2018 10:51:51 +0100
> > >>> Stefan Roese <sr@denx.de> wrote:
> > >>>        
> > >>>> Calling "mtdparts" currently fails when its called before any other mtd
> > >>>> command (or ubi command) has been called. The MTD devices are not
> > >>>> probed at this point and therefore it fails e.g. with this message:
> > >>>>       
> > >>>> => mtdparts    
> > >>>> Device spi-nand0 not found!    
> > >>>
> > >>> IIRC, we decided that mtdparts should not call mtd_probe_devices() to
> > >>> encourage people to stop using it.    
> > >>
> > >> I see. But I don't quite get how this missing call (and reslting
> > >> error message) would encourage people to stop using it.    
> > > 
> > > You're right, this message does not encourage people to stop using
> > > mtdparts on existing setups (mtdparts should work just fine on any MTD
> > > devices except SPI NANDs) but it does discourage them from using it on
> > > spi-nand devices since it returns an error.    
> > 
> > IMHO, that's more confusing than discouraging.
> >     
> > >>>>
> > >>>> This patch adds a call to mtd_probe_devices() to mtdparts_init() to
> > >>>> solve this issue. This also fixes a problem when calling "ubi part"
> > >>>> as first flash storage related command.    
> > >>>
> > >>> Hm, this one is unexpected. Miquel, any idea why this happens. Do we
> > >>> need to enable a specific option if we want mtd_probe_devices() to be
> > >>> called in the ubi part path?    
> > >>
> > >> Please note that "ubi part part-foo" does still work. It only
> > >> prints this error message before attaching the MTD partition.
> > >> The error is printed because of this call-chain:
> > >>
> > >> ubi_part()    
> > >> ->  ubi_detach()
> > >>       -> mtdparts_init()    
> > >>
> > >> So again, mtdparts_init() is called without the MTD devices
> > >> being probed.    
> > > 
> > > I guess we forgot to remove this mtdparts_init() call from the detach
> > > path. I think it's no longer needed since we now call
> > > mtd_probe_devices() in ubi_part(), and mtd_probe_devices() will take
> > > care of creating MTD partitions based on the mtdparts= and mtdids=
> > > variables.    
> > 
> > A quick test reveals that this removal does not remove the
> > error message. Instead the command does not work anymore at
> > all:
> >   
> > => ubi part nand    
> > Partition nand not found!
> > 
> > Before (and without my patch) its this:
> >   
> > => ubi part nand    
> > Device spi-nand0 not found!
> > Error initializing mtdparts!
> > ubi0: attaching mtd2
> > ubi0: scanning is finished
> > ubi0: attached mtd2 (name "nand", size 128 MiB)  
> 
> I think I found what's missing in mtd_probe_devices(): we don't use the
> default mtdparts and mtdids when those env vars are NULL (see what's
> done in mtdparts_init() to handle this case [1]).
> 
> [1]https://elixir.bootlin.com/u-boot/v2018.11-rc3/source/cmd/mtdparts.c#L1763

Isn't the right solution to always define these env variables when they
are needed? Defining such default behavior with a Kconfig entry is,
from my opinion, a lot of noise for such an useless feature...


Thanks,
Miquèl