Re: [PATCH v10 11/17] iio: frequency: ad9910: add basic parallel port support

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 29 Jul 2026 09:25:38 +0100
Rodrigo Alencar via B4 Relay <devnull+rodrigo.alencar.analog.com@kernel.org> wrote:

> From: Rodrigo Alencar <rodrigo.alencar@analog.com>
> 
> Add parallel port support with amplitude, phase and frequency channels.
> Those will be buffered capable channels, but only basic control of offset
> and scale are implemented at this point. There are separate amplitude
> and phase control for polar destination, which will provide different scan
> types. Enabling and disabling of parallel mode will be implemented with
> buffer setup ops or with update_scan_mode() once IIO backend integration
> is in place.
> 
> Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
Hmm. Curious... clang --version gives 22.1.8 on x86_64.

make LLVM=1 LOCALVERSION= -j12 W=1 C=1
  DESCEND objtool
Documentation/.renames.txt: warning: ignored by one of the .gitignore files
  CC [M]  drivers/iio/frequency/ad9910.o
In file included from drivers/iio/frequency/ad9910.c:10:
In file included from ./include/linux/clk.h:13:
In file included from ./include/linux/kernel.h:26:
In file included from ./include/linux/math.h:6:
./arch/x86/include/asm/div64.h:113:8: error: invalid operand for instruction
  113 |                 asm ("addq %[add], %[lo]; adcq $0, %[hi]" :
      |                      ^
<inline asm>:1:7: note: instantiated into assembly here
    1 |         addq $2147483648, %rax; adcq $0, %rdx
      |              ^~~~~~~~~~~~
1 error generated.
make[5]: *** [scripts/Makefile.build:289: drivers/iio/frequency/ad9910.o] Error 1
make[4]: *** [scripts/Makefile.build:549: drivers/iio/frequency] Error 2
make[3]: *** [scripts/Makefile.build:549: drivers/iio] Error 2
make[2]: *** [scripts/Makefile.build:549: drivers] Error 2
make[1]: *** [/home/jic23/src/kernel/iio/Makefile:2184: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2


> ---
>  drivers/iio/frequency/ad9910.c | 154 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 154 insertions(+)
> 
> diff --git a/drivers/iio/frequency/ad9910.c b/drivers/iio/frequency/ad9910.c
> index b41b011af281..aaeff2e7640e 100644
> --- a/drivers/iio/frequency/ad9910.c
> +++ b/drivers/iio/frequency/ad9910.c


>  static int ad9910_read_raw(struct iio_dev *indio_dev,
> @@ -691,6 +753,48 @@ static int ad9910_read_raw(struct iio_dev *indio_dev,
>  			*val = 0;
>  			*val2 = tmp64 >> 14;
>  			return IIO_VAL_INT_PLUS_NANO;
> +		case AD9910_CHAN_IDX_PARALLEL_PHASE:
> +			*val = 0;
> +			*val2 = AD9910_PI_NANORAD >> 15;
> +			return IIO_VAL_INT_PLUS_NANO;
> +		case AD9910_CHAN_IDX_PARALLEL_FREQ:
> +			tmp32 = FIELD_GET(AD9910_CFR2_FM_GAIN_MSK,
> +					  st->reg[AD9910_REG_CFR2].val32);
> +			tmp64 = (u64)st->data.sysclk_freq_hz << tmp32;
> +			tmp64 = ad9910_rational_scale(tmp64, NANO, BIT_ULL(32));

Process of elimination points me to this line which is a slim wrapper.

static inline u64 ad9910_rational_scale(u64 input, u64 scale, u64 reference)
{
	return mul_u64_add_u64_div_u64(input, scale, reference >> 1, reference);
}

David, any thoughts?

For now I'm backing out the series.

> +			*val = div_s64_rem(tmp64, NANO, val2);
> +			return IIO_VAL_INT_PLUS_NANO;
> +		case AD9910_CHAN_IDX_PARALLEL_POLAR_AMP:
> +			tmp64 = (u64)st->data.output_current_uA *
> +				AD9910_NANO_MILLIAMP_PER_MICROAMP;
> +			*val = 0;
> +			*val2 = tmp64 >> 8;
> +			return IIO_VAL_INT_PLUS_NANO;
> +		case AD9910_CHAN_IDX_PARALLEL_POLAR_PHASE:
> +			*val = 0;
> +			*val2 = AD9910_PI_NANORAD >> 7;
> +			return IIO_VAL_INT_PLUS_NANO;
> +		default:
> +			return -EINVAL;
> +		}