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Message-ID: <CABjd4YxZVQSuavEYojc8U4AqwUN3GkweiNNHqn=NDTE70xZm8w@mail.gmail.com>
Date: Wed, 21 May 2025 10:20:46 +0400
From: Alexey Charkov <alchark@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>, Rob Herring <robh@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>, Wim Van Sebroeck <wim@...ux-watchdog.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v4 4/4] watchdog: Add support for VIA/WonderMedia SoC
watchdog functionality
On Wed, May 21, 2025 at 3:15 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 5/20/25 13:01, Alexey Charkov wrote:
> > VIA/WonderMedia SoCs can use their system timer's first channel as a
> > watchdog device which will reset the system if the clocksource counter
> > matches the value given in its match register 0 and if the watchdog
> > function is enabled.
> >
> > Since the watchdog function is tightly coupled to the timer itself, it
> > is implemented as an auxiliary device of the timer device
> >
> > Signed-off-by: Alexey Charkov <alchark@...il.com>
> > ---
> > MAINTAINERS | 1 +
> > drivers/watchdog/Kconfig | 15 ++++++++
> > drivers/watchdog/Makefile | 1 +
> > drivers/watchdog/vt8500-wdt.c | 80 +++++++++++++++++++++++++++++++++++++++++++
> > 4 files changed, 97 insertions(+)
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 5362095240627f613638197fda275db6edc16cf7..97d1842625dbdf7fdca3556260662dab469ed091 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -3447,6 +3447,7 @@ F: drivers/tty/serial/vt8500_serial.c
> > F: drivers/video/fbdev/vt8500lcdfb.*
> > F: drivers/video/fbdev/wm8505fb*
> > F: drivers/video/fbdev/wmt_ge_rops.*
> > +F: drivers/watchdog/vt8500-wdt.c
> > F: include/linux/vt8500-timer.h
> >
> > ARM/ZYNQ ARCHITECTURE
> > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> > index 0d8d37f712e8cfb4bf8156853baa13c23a57d6d9..8049ae630301a98123f97f6e3ee868bd3bf1534a 100644
> > --- a/drivers/watchdog/Kconfig
> > +++ b/drivers/watchdog/Kconfig
> > @@ -2003,6 +2003,21 @@ config PIC32_DMT
> > To compile this driver as a loadable module, choose M here.
> > The module will be called pic32-dmt.
> >
> > +config VT8500_WATCHDOG
> > + tristate "VIA/WonderMedia VT8500 watchdog support"
> > + depends on ARCH_VT8500 || COMPILE_TEST
> > + select WATCHDOG_CORE
> > + select AUXILIARY_BUS
> > + help
> > + VIA/WonderMedia SoCs can use their system timer as a hardware
> > + watchdog, as long as the first timer channel is free from other
> > + uses and respective function is enabled in its registers. To
> > + make use of it, say Y here and ensure that the device tree
> > + lists at least two interrupts for the VT8500 timer device.
> > +
> > + To compile this driver as a module, choose M here.
> > + The module will be called vt8500-wdt.
> > +
> > # PARISC Architecture
> >
> > # POWERPC Architecture
> > diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> > index c9482904bf870a085c7fce2a439ac5089b6e6fee..3072786bf226c357102be3734fe6e701f753d45b 100644
> > --- a/drivers/watchdog/Makefile
> > +++ b/drivers/watchdog/Makefile
> > @@ -101,6 +101,7 @@ obj-$(CONFIG_MSC313E_WATCHDOG) += msc313e_wdt.o
> > obj-$(CONFIG_APPLE_WATCHDOG) += apple_wdt.o
> > obj-$(CONFIG_SUNPLUS_WATCHDOG) += sunplus_wdt.o
> > obj-$(CONFIG_MARVELL_GTI_WDT) += marvell_gti_wdt.o
> > +obj-$(CONFIG_VT8500_WATCHDOG) += vt8500-wdt.o
> >
> > # X86 (i386 + ia64 + x86_64) Architecture
> > obj-$(CONFIG_ACQUIRE_WDT) += acquirewdt.o
> > diff --git a/drivers/watchdog/vt8500-wdt.c b/drivers/watchdog/vt8500-wdt.c
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..54fe5ad7695de36f6b3c1d28e955f00bef00e9db
> > --- /dev/null
> > +++ b/drivers/watchdog/vt8500-wdt.c
> > @@ -0,0 +1,80 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (C) 2025 Alexey Charkov <alchark@...il.com */
> > +
> > +#include <linux/auxiliary_bus.h>
> > +#include <linux/container_of.h>
> > +#include <linux/io.h>
> > +#include <linux/limits.h>
> > +#include <linux/module.h>
> > +#include <linux/types.h>
> > +#include <linux/watchdog.h>
> > +#include <linux/vt8500-timer.h>
> > +
> > +static int vt8500_watchdog_start(struct watchdog_device *wdd)
> > +{
> > + struct vt8500_wdt_info *info = watchdog_get_drvdata(wdd);
> > + u64 deadline = info->timer_next(wdd->timeout * VT8500_TIMER_HZ);
> > +
>
> wdd->timeout is the soft timeout, which may be larger
> than the maximum hardware timeout. That means you'll need
> to use something like "min(wdd->timeout, U32_MAX / VT8500_TIMER_HZ)
> * VT8500_TIMER_HZ" as parameter to the timer_next call.
Indeed. For some reason I thought the core splits up large user
requested timeout values into at most max_hw_heartbeat_ms long chunks
and feeds those to the driver via the timeout field, but now I see it
doesn't.
Do I get it right that the core worker will try and do its last ping
of the hardware at exactly max_hw_heartbeat_ms before the user
specified deadline?
> > + writel((u32)deadline, info->wdt_match);
>
> Can deadline overflow ?
Yes. The underlying hardware counter is a u32 value incrementing at
VT8500_TIMER_HZ and continuing past wraparound. This register sets the
next match value: once the hardware counter reaches the value of
(u32)deadline (which might be after the counter wrapping around iff
deadline > U32_MAX) the system resets. Perhaps it warrants a comment
in code.
Thanks for your review, Guenter!
Best regards,
Alexey
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