linux-kernel - Re: [PATCH 03/28] nvmem: add a notifier chain

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Date:   Wed, 8 Aug 2018 18:30:49 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Jonathan Corbet <corbet@....net>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Naren <naren.kernel@...il.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lukas Wunner <lukas@...ner.de>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Sven Van Asbroeck <svendev@...x.com>,
        Paolo Abeni <pabeni@...hat.com>, Alban Bedel <albeu@...e.fr>,
        Rob Herring <robh@...nel.org>,
        David Lechner <david@...hnology.com>,
        linux-doc <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        linux-mtd@...ts.infradead.org,
        Linux-OMAP <linux-omap@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 03/28] nvmem: add a notifier chain

2018-08-08 18:13 GMT+02:00 Andrew Lunn <andrew@...n.ch>:
> On Wed, Aug 08, 2018 at 05:31:25PM +0200, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@...libre.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