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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Wed, 8 Aug 2018 18:30:49 +0200
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Subject: Re: [PATCH 03/28] nvmem: add a notifier chain
To:     Andrew Lunn <andrew@lunn.ch>
Cc:     Bartosz Golaszewski <brgl@bgdev.pl>,
        Jonathan Corbet <corbet@lwn.net>, Sekhar Nori <nsekhar@ti.com>,
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2018-08-08 18:13 GMT+02:00 Andrew Lunn <andrew@lunn.ch>:
> On Wed, Aug 08, 2018 at 05:31:25PM +0200, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>>
>> Add a blocking notifier chain with two events (add and remove) so that
>> users can get notified about the addition of nvmem devices they're
>> waiting for.
>>
>> We'll use this instead of the at24 setup callback in the mityomapl138
>> board file.
>
> Hi Bartosz
>
> What context is this notifier chain called in?
>
> I did something similar using the i2c notifier to try to work around
> the impending disappearing of the setup callback. But i got lockdep
> splats, because the notifier was called while some locks were being
> held, so it was not possible to register other i2c devices.
>
> The at24 setup callback is done as part of probe, so no important
> locks are held. Are any locks held when this notifier chain is called?
>
> Thanks
>         Andrew

In the case of at24 it would be called from at24_probe() ->
nvmem_register() in process context. Would you mind testing it? Would
be great to see if it works on multiple setups.

Bart