linux-kernel - Re: [PATCH v3 3/4] clocksource/drivers/timer-vt8500: Prepare for watchdog functionality

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Message-ID: <CABjd4YwJgZiq9_jKGa70GaxaW8TT=JuwDioU6jH=J_O=t+QT8w@mail.gmail.com>
Date: Mon, 19 May 2025 15:34:59 +0400
From: Alexey Charkov <alchark@...il.com>
To: kernel test robot <lkp@...el.com>
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>, 
	Wim Van Sebroeck <wim@...ux-watchdog.org>, Guenter Roeck <linux@...ck-us.net>, 
	oe-kbuild-all@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v3 3/4] clocksource/drivers/timer-vt8500: Prepare for
 watchdog functionality

On Sun, May 18, 2025 at 5:24 AM kernel test robot <lkp@...el.com> wrote:
>
> Hi Alexey,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on 92a09c47464d040866cf2b4cd052bc60555185fb]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Alexey-Charkov/dt-bindings-timer-via-vt8500-timer-Convert-to-YAML/20250516-025729
> base:   92a09c47464d040866cf2b4cd052bc60555185fb
> patch link:    https://lore.kernel.org/r/20250515-vt8500-timer-updates-v3-3-2197a1b062bd%40gmail.com
> patch subject: [PATCH v3 3/4] clocksource/drivers/timer-vt8500: Prepare for watchdog functionality
> config: loongarch-randconfig-r123-20250517 (https://download.01.org/0day-ci/archive/20250518/202505180911.hDevFA1N-lkp@intel.com/config)
> compiler: loongarch64-linux-gcc (GCC) 14.2.0
> reproduce: (https://download.01.org/0day-ci/archive/20250518/202505180911.hDevFA1N-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202505180911.hDevFA1N-lkp@intel.com/
>
> sparse warnings: (new ones prefixed by >>)
> >> drivers/clocksource/timer-vt8500.c:201:51: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected void *platform_data @@     got void [noderef] __iomem *static [assigned] [toplevel] regbase @@
>    drivers/clocksource/timer-vt8500.c:201:51: sparse:     expected void *platform_data
>    drivers/clocksource/timer-vt8500.c:201:51: sparse:     got void [noderef] __iomem *static [assigned] [toplevel] regbase
>
> vim +201 drivers/clocksource/timer-vt8500.c
>
>    175
>    176  /*
>    177   * This probe gets called after the timer is already up and running. This will create
>    178   * the watchdog device as a child since the registers are shared.
>    179   */
>    180  static int vt8500_timer_probe(struct platform_device *pdev)
>    181  {
>    182          struct platform_device *vt8500_watchdog_device;
>    183          struct device *dev = &pdev->dev;
>    184          int ret;
>    185
>    186          if (!sys_timer_ch) {
>    187                  dev_info(dev, "Not enabling watchdog: only one irq was given");
>    188                  return 0;
>    189          }
>    190
>    191          if (!regbase)
>    192                  return dev_err_probe(dev, -ENOMEM,
>    193                          "Timer not initialized, cannot create watchdog");
>    194
>    195          vt8500_watchdog_device = platform_device_alloc("vt8500-wdt", -1);
>    196          if (!vt8500_watchdog_device)
>    197                  return dev_err_probe(dev, -ENOMEM,
>    198                          "Failed to allocate vt8500-wdt");
>    199
>    200          /* Pass the base address as platform data and nothing else */
>  > 201          vt8500_watchdog_device->dev.platform_data = regbase;

Frankly, given that this driver only applies to VT8500 (which is ARM
based), the warning appears a bit overzealous. After all, on ARM MMIO
addresses are in the same physical address space as normal memory
addresses, and furthermore this platform_data is never dereferenced
directly anyway.

I could silence the warning either by more aggressive casting or by
wrapping the pointer into some struct, but both of those sound a bit
overreaching. Would appreciate guidance from the list on how to best
approach this.

Best regards,
Alexey