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

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Date:   Mon, 25 Jun 2018 19:40:24 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Bartosz Golaszewski <brgl@...ev.pl>
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-kernel@...ts.infradead.org, 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

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