Re: [PATCH 2/2] watchdog: Add the Software Watchdog Timer for the NXP S32 platform
From: Daniel Lezcano
Date: Fri Mar 28 2025 - 16:58:20 EST
On 28/03/2025 20:56, Guenter Roeck wrote:
On 3/28/25 12:42, Daniel Lezcano wrote:
Hi Guenter,
thanks for your review
On 28/03/2025 19:10, Guenter Roeck wrote:
On 3/28/25 08:15, Daniel Lezcano wrote:
The S32 platform has several Software Watchdog Timer available and
Why "Software" ? This is a hardware watchdog, or am I missing
something ?
I have no idea why it is called 'Software' because it is indeed a
hardware watchdog. It is how NXP called it in their technical
reference manual.
I guess it is because it resets the software. Please drop the term;
it is misleading.
Ok, I will drop the term but keep a reference to the NXP documentation.
tied with a CPU. The SWT0 is the only one which directly asserts the
reset line, other SWT require an external setup to configure the reset
behavior which is not part of this change.
The maximum watchdog value depends on the clock feeding the SWT
counter which is 32bits wide. On the s32g274-rb2, the clock has a rate
of 51MHz which lead to 83 seconds maximum timeout.
The timeout can be specified via the device tree with the usual
existing bindings 'timeout-sec' or via the module param timeout.
The watchdog can be loaded with the 'nowayout' option, preventing the
watchdog to be stopped.
The watchdog can be started at boot time with the 'early-enable'
option, thus letting the watchdog framework to service the watchdog
counter.
the watchdog support the magic character to stop when the userspace
releases the device.
Cc: Ghennadi Procopciuc <ghennadi.procopciuc@xxxxxxx>
Cc: Thomas Fossati <thomas.fossati@xxxxxxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
---
[ ... ]
--- /dev/null
+++ b/drivers/watchdog/s32g_wdt.c
@@ -0,0 +1,362 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Watchdog driver for S32G SoC
+ *
+ * Copyright (C) 2014 Freescale Semiconductor, Inc.
+ * Copyright 2017-2019, 2021-2025 NXP.
Does this originate from out-of-tree code ?
If so, a reference would be helpful.
Well, I kept the copyright but this implementation is mostly from
scratch.
I am not a copyright expert, but if this isn't derived from some other
driver
it should not include old copyrights.
Ok, I'll put only the NXP copyright
[ ... ]
+static void s32g_wdt_debugfs_init(struct device *dev, struct
s32g_wdt_device *wdev)
+{
+ struct debugfs_regset32 *regset;
+ static struct dentry *dentry = NULL;
+
+ if (!dentry)
+ dentry = debugfs_create_dir("watchdog", NULL);
That is a terribly generic debugfs directory name. That is unacceptable.
Pick a name that is driver specific.
Why is it terrible ? We end up with:
watchdog/40100000.watchdog
There are 7 watchdogs on the platform, the directory is there to group
them all. It seems to me it is self-explanatory, no ?
It should be something like "s32g/40100000.watchdog". Someone could have
some other watchdog
(say, a real software watchdog) in the system and decide to use the top
level directory name
for whatever reason. The top level should be something driver specific,
not a generic name.
Apparently we can have a subsystem creating the subsystem directory.
For example regmap is created by the core framework:
ls /sys/kernel/debug/regmap
4009c240.pinctrl-map0 4009c240.pinctrl-map1 4009c240.pinctrl-map2
4009c240.pinctrl-map3 4009c240.pinctrl-map4 4009c240.pinctrl-map5
drivers/base/regmap/regmap-debugfs.c
regmap_debugfs_root = debugfs_create_dir("regmap", NULL);
Or pinctrl:
ls /sys/kernel/debug/pinctrl
4009c240.pinctrl pinctrl-devices pinctrl-handles pinctrl-maps
drivers/pinctrl/core.c:
debugfs_root = debugfs_create_dir("pinctrl", NULL);
Would it make sense to have the watchdog framework to create this
topmost directory and have the driver to use an API like:
int watchdog_debugfs_add(struct watchdog_device *wdog);
with wdog->debugfs set by the caller.
No need to have more API. When the driver is unloaded it can destroy its
own directory. And when the core watchdog framework exits, it can
recursively destroy the topmost directory.
+
+ dentry = debugfs_create_dir(dev_name(dev), dentry);
+
Where is this removed if the driver is unloaded ?
Oh right, I missed it. Thanks for pointing this out.
Also, if the driver is built into the kernel, it seems to me that a
second
instance will create a nested directory. That seems odd.
No, because there is the test above if (!dentry) which is a static
variable.
Yes, and then the second watchdog will create
"watchdog/40100000.watchdog/40200000.watchdog"
or similar because dentry is overwritten with the reference to
"40100000.watchdog"
Thanks,
Guenter
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