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

[Boris Brezillon]

On Tue, 30 Oct 2018 11:59:13 +0100
Stefan Roese <sr at denx.de> wrote:

> On 30.10.18 11:41, Boris Brezillon wrote:
> > On Tue, 30 Oct 2018 11:13:37 +0100
> > Stefan Roese <sr at 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 at 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