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Date:   Tue, 30 Jul 2019 08:57:37 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     linux-watchdog@cger.kernel.org,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Marking legacy watchdog drivers as deprecated / obsolete
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On Tue, Jul 30, 2019 at 10:00:36AM +0200, Arnd Bergmann wrote:
> On Tue, Jul 30, 2019 at 12:07 AM Guenter Roeck <linux@roeck-us.net> wrote:
> >
> > Hi,
> >
> > we have recently seen a number of changes to legacy watchdog drivers,
> > mostly surrounding the coding style used some 10+ years ago, but also
> > fixing minor formatting or coding problems found by static analyzers.
> > This slowly rises above the level of background noise.
> >
> > Would it be acceptable to mark all those drivers as deprecated/obsolete,
> > warn users that the driver should be converted to use the watchdog
> > subsystem, and that it will otherwise be removed in a later Linux kernel
> > version ? This would give us an idea which drivers are still in use,
> > and it would enable us to remove the remaining drivers maybe 5 or 6
> > releases for now.
> >
> > Thoughts ?
> 
> I don't think an automated approach across 61 drivers is likely to work
> well. About half of the drivers appear to be for specific SoCs, and
> removing the watchdog driver while keeping the rest of the SoC support
> would not be helpful, it  just means we break one of the drivers for the
> last remaining users of an old SoC the next time they try to upgrade to
> a new kernel.
> 

The primary goal would be to identify drivers still in use, and to trigger
efforts to convert those drivers to the new infrastructure. Removal of
obsolete / unused drivers would be a separate decision, to be made at some
point in the future, and individually for each driver. I specifically wasn't
trying to suggest auto-removal.

Guenter

> It would probably be helpful to go through the list and see if any of
> the drivers
> are for platforms that are already gone. FWIW, here is the list of drivers that
> have their own .ioctl() method, taken from a patch I'm sending soon
> to add a .compat_ioctl handler:
> 
> arch/powerpc/platforms/52xx/mpc52xx_gpt.c
> arch/um/drivers/harddog_kern.c
> drivers/char/ipmi/ipmi_watchdog.c
> drivers/hwmon/fschmd.c
> drivers/rtc/rtc-ds1374.c
> drivers/watchdog/acquirewdt.c
> drivers/watchdog/advantechwdt.c
> drivers/watchdog/alim1535_wdt.c
> drivers/watchdog/alim7101_wdt.c
> drivers/watchdog/ar7_wdt.c
> drivers/watchdog/at91rm9200_wdt.c
> drivers/watchdog/ath79_wdt.c
> drivers/watchdog/bcm63xx_wdt.c
> drivers/watchdog/cpu5wdt.c
> drivers/watchdog/eurotechwdt.c
> drivers/watchdog/f71808e_wdt.c
> drivers/watchdog/gef_wdt.c
> drivers/watchdog/geodewdt.c
> drivers/watchdog/ib700wdt.c
> drivers/watchdog/ibmasr.c
> drivers/watchdog/indydog.c
> drivers/watchdog/intel_scu_watchdog.c
> drivers/watchdog/iop_wdt.c
> drivers/watchdog/it8712f_wdt.c
> drivers/watchdog/ixp4xx_wdt.c
> drivers/watchdog/ks8695_wdt.c
> drivers/watchdog/m54xx_wdt.c
> drivers/watchdog/machzwd.c
> drivers/watchdog/mixcomwd.c
> drivers/watchdog/mtx-1_wdt.c
> drivers/watchdog/mv64x60_wdt.c
> drivers/watchdog/nuc900_wdt.c
> drivers/watchdog/nv_tco.c
> drivers/watchdog/pc87413_wdt.c
> drivers/watchdog/pcwd.c
> drivers/watchdog/pcwd_pci.c
> drivers/watchdog/pcwd_usb.c
> drivers/watchdog/pika_wdt.c
> drivers/watchdog/pnx833x_wdt.c
> drivers/watchdog/rc32434_wdt.c
> drivers/watchdog/rdc321x_wdt.c
> drivers/watchdog/riowd.c
> drivers/watchdog/sa1100_wdt.c
> drivers/watchdog/sb_wdog.c
> drivers/watchdog/sbc60xxwdt.c
> drivers/watchdog/sbc7240_wdt.c
> drivers/watchdog/sbc_epx_c3.c
> drivers/watchdog/sbc_fitpc2_wdt.c
> drivers/watchdog/sc1200wdt.c
> drivers/watchdog/sc520_wdt.c
> drivers/watchdog/sch311x_wdt.c
> drivers/watchdog/scx200_wdt.c
> drivers/watchdog/smsc37b787_wdt.c
> drivers/watchdog/w83877f_wdt.c
> drivers/watchdog/w83977f_wdt.c
> drivers/watchdog/wafer5823wdt.c
> drivers/watchdog/wdrtas.c
> drivers/watchdog/wdt.c
> drivers/watchdog/wdt285.c
> drivers/watchdog/wdt977.c
> drivers/watchdog/wdt_pci.c
> 
>       Arnd