Messages in this thread |  | | From | Alexey Charkov <> | | Date | Wed, 21 May 2025 10:20:46 +0400 | | Subject | Re: [PATCH v4 4/4] watchdog: Add support for VIA/WonderMedia SoC watchdog functionality |
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On Wed, May 21, 2025 at 3:15 AM Guenter Roeck <linux@roeck-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@gmail.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@gmail.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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