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Date:   Mon, 27 Apr 2020 16:37:11 +0200
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     Ricardo Ribalda Delgado <ribalda@kernel.org>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd@lists.infradead.org, LKML <linux-kernel@vger.kernel.org>,
        Tudor Ambarus <tudor.ambarus@microchip.com>
Subject: Re: [PATCH v2] mtd: Fix mtd not the same name not registered if
 nvmem
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On Mon, 27 Apr 2020 16:22:22 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> Hi Ricardo,
> 
> Ricardo Ribalda Delgado <ribalda@kernel.org> wrote on Tue, 14 Apr 2020
> 15:47:23 +0200:
> 
> > Ping?
> > 
> > On Thu, Apr 2, 2020 at 8:59 AM Ricardo Ribalda Delgado
> > <ribalda@kernel.org> wrote:  
> > >
> > > When the nvmem framework is enabled, a nvmem device is created per mtd
> > > device/partition.
> > >
> > > It is not uncommon that a device can have multiple mtd devices with
> > > partitions that have the same name. Eg, when there DT overlay is allowed
> > > and the same device with mtd is attached twice.
> > >
> > > Under that circumstances, the mtd fails to register due to a name
> > > duplication on the nvmem framework.
> > >
> > > With this patch we add a _1, _2, _X to the subsequent names if there is
> > > a collition, and throw a warning, instead of not starting the mtd
> > > device.
> > >
> > > [    8.948991] sysfs: cannot create duplicate filename '/bus/nvmem/devices/Production Data'
> > > [    8.948992] CPU: 7 PID: 246 Comm: systemd-udevd Not tainted 5.5.0-qtec-standard #13
> > > [    8.948993] Hardware name: AMD Dibbler/Dibbler, BIOS 05.22.04.0019 10/26/2019
> > > [    8.948994] Call Trace:
> > > [    8.948996]  dump_stack+0x50/0x70
> > > [    8.948998]  sysfs_warn_dup.cold+0x17/0x2d
> > > [    8.949000]  sysfs_do_create_link_sd.isra.0+0xc2/0xd0
> > > [    8.949002]  bus_add_device+0x74/0x140
> > > [    8.949004]  device_add+0x34b/0x850
> > > [    8.949006]  nvmem_register.part.0+0x1bf/0x640
> > > ...
> > > [    8.948926] mtd mtd8: Failed to register NVMEM device
> > >
> > > Signed-off-by: Ricardo Ribalda Delgado <ribalda@kernel.org>  
> 
> Thanks for proposing this change. Indeed we are aware of the problem
> and the best solution that we could come up with was to create an
> additional "unique_name" field to the mtd_info structure. This new
> field would have the form:
> 
>     [<parent-unique-name><separator>]<mtd-name>
> 
> The separator might be '~' (but I am completely open on that), and that
> would give for instance:
> 
>     my-controller~my-device~my-part~mysub-part

I'd prefer something slightly more standard for the separator, like '/',
which is what we usually use when we want to represent a path in a tree.
I do agree on the general approach though.

Note that controller name is normally hidden in the root MTD device
name, and it's the driver responsibility to come up with a name that
does not collide with other MTD drivers. We can of course try to pick a
different name if we see another device with the same name, but we
should definitely warn about that so drivers are patched accordingly.