Re: [PATCH v5 09/14] iio: magnetometer: yas530: Introduce "chip_info" structure

From: Nathan Chancellor <nathan@kernel.org>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: kernel test robot <lkp@intel.com>,
	Jakob Hauser <jahau@rocketmail.com>,
	Jonathan Cameron <jic23@kernel.org>,
	llvm@lists.linux.dev, kbuild-all@lists.01.org,
	Lars-Peter Clausen <lars@metafoo.de>,
	Linus Walleij <linus.walleij@linaro.org>,
	Hans de Goede <hdegoede@redhat.com>,
	linux-iio <linux-iio@vger.kernel.org>,
	devicetree <devicetree@vger.kernel.org>,
	phone-devel@vger.kernel.org,
	~postmarketos/upstreaming@lists.sr.ht
Subject: Re: [PATCH v5 09/14] iio: magnetometer: yas530: Introduce "chip_info" structure
Date: Mon, 8 Aug 2022 08:59:50 -0700	[thread overview]
Message-ID: <YvEy9uq49ZiBHtFd@dev-arch.thelio-3990X> (raw)
In-Reply-To: <CAHp75VecMvtHwkA6=JxHbX0oeRg+-fXNraggBCaOxqhf9WUdzQ@mail.gmail.com>

Hi Andy,

On Mon, Aug 08, 2022 at 01:18:06PM, +0200, Andy Shevchenko wrote:
> On Mon, Aug 8, 2022 at 7:40 AM kernel test robot <lkp@intel.com> wrote:
> 
> ...
> 
> > All errors (new ones prefixed by >>):
> >
> > >> drivers/iio/magnetometer/yamaha-yas530.c:933:19: error: initializer element is not a compile-time constant
> >                    .product_name = yas5xx_product_name[yas530],
> >                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> >    1 error generated.
> 
> What?!
> 
> The yas530 is a part of the enum, how come that compiler can't see
> this? Looks like a Clang bug.

That is not what clang is complaining about here, you'll see the same
error even if you used '0', '1', or '2' here:

  drivers/iio/magnetometer/yamaha-yas530.c:933:19: error: initializer element is not a compile-time constant
                  .product_name = yas5xx_product_name[0],
                                  ^~~~~~~~~~~~~~~~~~~~~~
  1 error generated.

It is complaining that the initializer element
('yas5xx_product_name[yas530]', rather than just 'yas530') is not
constant, which is a true complaint if I am reading C11 standard 6.6.7
correctly.

GCC 8+ has chosen to accept const structures as constant expressions in
designated initializers, which it is allowed to do per 6.6.10. Nick did
have a patch to try and match this behavior in clang but the work that
was requested doesn't seem to be trivial so it was never finalized:
https://reviews.llvm.org/D76096

You'll see the same error with GCC 7:

  drivers/iio/magnetometer/yamaha-yas530.c:933:19: error: initializer element is not constant
     .product_name = yas5xx_product_name[yas530],
                     ^~~~~~~~~~~~~~~~~~~
  drivers/iio/magnetometer/yamaha-yas530.c:933:19: note: (near initialization for ‘yas5xx_chip_info_tbl[0].product_name’)
  drivers/iio/magnetometer/yamaha-yas530.c:938:19: error: initializer element is not constant
     .product_name = yas5xx_product_name[yas532],
                     ^~~~~~~~~~~~~~~~~~~
  drivers/iio/magnetometer/yamaha-yas530.c:938:19: note: (near initialization for ‘yas5xx_chip_info_tbl[1].product_name’)
  drivers/iio/magnetometer/yamaha-yas530.c:943:19: error: initializer element is not constant
     .product_name = yas5xx_product_name[yas533],
                     ^~~~~~~~~~~~~~~~~~~
  drivers/iio/magnetometer/yamaha-yas530.c:943:19: note: (near initialization for ‘yas5xx_chip_info_tbl[2].product_name’)

Cheers,
Nathan

> >    930  static const struct yas5xx_chip_info yas5xx_chip_info_tbl[] = {
> >    931          [yas530] = {
> >    932                  .devid = YAS530_DEVICE_ID,
> >  > 933                  .product_name = yas5xx_product_name[yas530],
> >    934                  .version_name = yas5xx_version_names[yas530],
> >    935          },
> >    936          [yas532] = {
> >    937                  .devid = YAS532_DEVICE_ID,
> >    938                  .product_name = yas5xx_product_name[yas532],
> >    939                  .version_name = yas5xx_version_names[yas532],
> >    940          },
> >    941          [yas533] = {
> >    942                  .devid = YAS532_DEVICE_ID,
> >    943                  .product_name = yas5xx_product_name[yas533],
> >    944                  .version_name = yas5xx_version_names[yas533],
> >    945          },
> >    946  };
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 