linux-kernel - Re: [PATCH 00/14] ARM: davinci: step towards removing at24_platform

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Date:   Mon, 25 Jun 2018 19:46:51 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Sekhar Nori <nsekhar@...com>, Kevin Hilman <khilman@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Lukas Wunner <lukas@...ner.de>, Rob Herring <robh@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        David Lechner <david@...hnology.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-omap@...r.kernel.org, netdev@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 00/14] ARM: davinci: step towards removing at24_platform_data

2018-06-25 19:40 GMT+02:00 Andrew Lunn <andrew@...n.ch>:
> On Mon, Jun 25, 2018 at 05:50:11PM +0200, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>
>> Since I took over maintainership of the at24 driver I've been working
>> towards removing at24_platform_data in favor for device properties.
>>
>> DaVinci is the only platform that's still using it - all other users
>> have already been converted.
>>
>> One of the obstacles in case of DaVinci is removing the setup() callback
>> from the pdata struct, the only user of which are some davinci boards.
>
> Hi Bartosz
>
> Nice code.
>
> I've got a platform i want to add sometime soon using the at24. I
> noticed you doing the cleanup, so i avoided the setup() call. But
> using it would of helped...
>
> My platform is x86 based, so no device tree. I instantiate a number of
> AT24 devices from a platform driver, and then add nvmem cells so i can
> access data in these eeproms. This new code will make this simpler.
>
>> The only board that's still using this callback is now mityomapl138.
>> Unfortunately it stores more info in EEPROM than just the MAC address
>> and will require some more work. Unfortunately I don't have access
>> to this board so I can't test any actual solutions on a live hardware.
>
> Depending on what i find in the EEPROM, i need to instantiate other
> i2c devices. So i have the problem of knowing when the EEPROM has
> actually probed and i can use the nvmem API to retrieve the contents.
>
> What i have done so far, is registers a bus notifier on i2c_bus_type,
> and look for BUS_NOTIFY_BOUND_DRIVER. I can then check if the i2c
> client in the notifier is the at24 client. But when i then add more
> i2c clients from inside the notifier i get lockdep splats. They are
> false positives, but it does suggest it is not a good idea to do this.
>
> So it would be good to have some sort of recommended alternative to
> the setup() callback. Ideally it would be specific to a particular
> at24, and safe to call other i2c functions from.
>
> Do you have any ideas?
>
>    Andrew

With my patch 1/14 you'll get -EPROBE_DEFER from nvmem_cell_get() if
the nvmem provider is not yet registered. Will that help in your case?

Bart