linux-kernel - Re: [PATCH 3/5] iio: mcp9600: Recognize chip id for mcp9601

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Message-ID: <20250818150659.GA2948920@ax162>
Date: Mon, 18 Aug 2025 08:06:59 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Jonathan Cameron <jic23@...nel.org>
Cc: kernel test robot <lkp@...el.com>, Ben Collins <bcollins@...ter.com>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, llvm@...ts.linux.dev,
	oe-kbuild-all@...ts.linux.dev, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] iio: mcp9600: Recognize chip id for mcp9601

Hi Jonathan,

On Sat, Aug 16, 2025 at 11:02:43AM +0100, Jonathan Cameron wrote:
> On Sat, 16 Aug 2025 16:46:12 +0800
> kernel test robot <lkp@...el.com> wrote:
> 
> > Hi Ben,
> > 
> > kernel test robot noticed the following build warnings:
> > 
> > [auto build test WARNING on jic23-iio/togreg]
> > [also build test WARNING on linus/master v6.17-rc1 next-20250815]
> > [If your patch is applied to the wrong git tree, kindly drop us a note.
> > And when submitting patch, we suggest to use '--base' as documented in
> > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Ben-Collins/dt-bindings-iio-mcp9600-Add-compatible-for-microchip-mcp9601/20250816-005705
> > base:   https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
> > patch link:    https://lore.kernel.org/r/20250815164627.22002-4-bcollins%40watter.com
> > patch subject: [PATCH 3/5] iio: mcp9600: Recognize chip id for mcp9601
> > config: riscv-randconfig-001-20250816 (https://download.01.org/0day-ci/archive/20250816/202508161646.PDl6V4EU-lkp@intel.com/config)
> > compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 93d24b6b7b148c47a2fa228a4ef31524fa1d9f3f)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250816/202508161646.PDl6V4EU-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/202508161646.PDl6V4EU-lkp@intel.com/
> > 
> > All warnings (new ones prefixed by >>):

<trim unrelated -Wnull-pointer-arithmetic>

> > >> drivers/iio/temperature/mcp9600.c:440:53: warning: invalid conversion specifier '\x0a' [-Wformat-invalid-specifier]  
> >      440 |                                 "Expected id %02x, but device responded with %02\n",
> >          |                                                                              ~~~^
> >    include/linux/dev_printk.h:156:62: note: expanded from macro 'dev_warn'
> >      156 |         dev_printk_index_wrap(_dev_warn, KERN_WARNING, dev, dev_fmt(fmt), ##__VA_ARGS__)
> >          |                                                                     ^~~
> >    include/linux/dev_printk.h:19:22: note: expanded from macro 'dev_fmt'
> >       19 | #define dev_fmt(fmt) fmt
> >          |                      ^~~
> >    include/linux/dev_printk.h:110:16: note: expanded from macro 'dev_printk_index_wrap'
> >      110 |                 _p_func(dev, fmt, ##__VA_ARGS__);                       \
> >          |                              ^~~
> > >> drivers/iio/temperature/mcp9600.c:441:26: warning: data argument not used by format string [-Wformat-extra-args]  
> >      440 |                                 "Expected id %02x, but device responded with %02\n",
> >          |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >      441 |                                  chip_info->chip_id, dev_id);
> >          |                                                      ^
> >    include/linux/dev_printk.h:156:70: note: expanded from macro 'dev_warn'
> >      156 |         dev_printk_index_wrap(_dev_warn, KERN_WARNING, dev, dev_fmt(fmt), ##__VA_ARGS__)
> >          |                                                                     ~~~     ^
> >    include/linux/dev_printk.h:110:23: note: expanded from macro 'dev_printk_index_wrap'
> >      110 |                 _p_func(dev, fmt, ##__VA_ARGS__);                       \
> >          |                              ~~~    ^
> >    drivers/iio/temperature/mcp9600.c:428:22: warning: unused variable 'ret' [-Wunused-variable]
> >      428 |         int ch_sel, dev_id, ret;
> >          |                             ^~~
> >    10 warnings generated.
> > 
> > 
> > vim +/x0a +440 drivers/iio/temperature/mcp9600.c
> > 
> >    422	
> >    423	static int mcp9600_probe(struct i2c_client *client)
> >    424	{
> >    425		const struct mcp_chip_info *chip_info = i2c_get_match_data(client);
> 
> Probably a false positive as I don't think we can probe without something matching and hence
> that not being NULL but an error check on that match is still a nice to have and should
> resolve this build warning.  Note there is very little chance a compiler could ever figure
> out if this can be NULL or not so it's a reasonable warning!

I am not sure I follow if you are referring to the -Wformat warnings
above. Isn't it pointing out that the second specifier is missing the
actual type? Shouldn't it be '%02x' or something of the sort?

Cheers,
Nathan