linux-kernel - Re: [PATCH 1/5] watchdog: Create watchdog device in watchdog

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Date:	Tue, 22 Dec 2015 08:15:41 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Damien Riegel <damien.riegel@...oirfairelinux.com>,
	linux-watchdog@...r.kernel.org, Wim Van Sebroeck <wim@...ana.be>,
	Pratyush Anand <panand@...hat.com>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] watchdog: Create watchdog device in watchdog_dev.c

On 12/22/2015 07:33 AM, Damien Riegel wrote:
> On Mon, Dec 21, 2015 at 03:28:39PM -0800, Guenter Roeck wrote:
>> On 12/21/2015 09:31 AM, Damien Riegel wrote:
>>> On Sun, Dec 20, 2015 at 01:04:59PM -0800, Guenter Roeck wrote:
>>>> The watchdog character device is currently created in watchdog_dev.c,
>>>> and the watchdog device in watchdog_core.c. This results in
>>>> cross-dependencies, since device creation needs to know the watchdog
>>>> character device number as well as the watchdog class, both of which
>>>> reside in watchdog_dev.c.
>>>>
>>>> Create the watchdog device in watchdog_dev.c to simplify the code.
>>>>
>>>> Inspired by earlier patch set from Damien Riegel.
>>>
>>> Hi Guenter,
>>>
>>> The main purpose of my patch was to inverse the device creation and the
>>> cdev registration to avoid a racy situation, bu you have dropped that in
>>> this version. Is there a reason for that?
>>>
>> Every other driver I looked at does it in the same order (cdev first, device
>> second). I don't really know if doing it differently has any undesired
>> side effect, so I wanted to play safe.
>>
>> It would help a lot if someone listening to this exchange can confirm
>> that it is ok to create the device first, followed by the character device.
>
> The issue is that some drivers use watchdog_device->dev in their
> watchdog_ops functions. With a quick grep, I could spot 3 examples:
>
>   - bcm2835_wdt_stop in bcm2835_wdt.c
>   - gpio_wdt_hwping in gpio_wdt.c
>   - a21_wdt_set_timeout in mena21_wdt.c
>
> Maybe we should simply fix these drivers and keep watchdog_device->dev
> for core internal usage?
>

Yes, I have been thinking about that - essentially move the ->dev pointer
to the internal data structure and either use pr_ functions in those drivers,
or save a pointer to the platform device (if available) and use it.

I think I'll start working on a follow-up patch set to do just that.

Guenter

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