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

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Date:	Tue, 22 Dec 2015 10:33:37 -0500
From:	Damien Riegel <damien.riegel@...oirfairelinux.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	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 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?


Thanks,
Damien
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