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

[David Laight <david.laight.linux@gmail.com>]

On Sun, 2 Aug 2026 01:56:07 +0100
Jonathan Cameron <jic23@kernel.org> wrote:

> 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?

Lots of instructions only support sign extending 32bit immediates.
The asm constraint for the ADCQ needs to be "erm" not "irm".
I bet that is true elsewhere as well.

See source/arch/x86/include/asm/div64.h line 114

I'm actually surprised you see it with clang - it usually prefers the "m"
constraint.

I'll try to find a source tree that is clean enough to generate a patch.

	David


> 
> 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;
> > +		}