Re: [PATCH v4 1/2] iio: filter: admv8818: fix range calculation

Jonathan Cameron
2025-03-04T23:55:16Z

On Tue, 25 Feb 2025 08:46:11 -0500
Sam Winchenbach <sam.winchenbach@framepointer.org> wrote:

Hi Sam,

Various comments inline.

Jonathan

> Corrects the upper range of LPF Band 4 from 18.5 GHz to 18.85 GHz per
> the ADMV8818 datasheet
This feels like a first fix...
>
> Search for the minimum error while ensuring that the LPF corner
> frequency is greater than the target, and the HPF corner frequency
> is lower than the target
>
> This fixes issues where the range calculations were suboptimal.
This feels like a 2nd one. Maybe two patches appropriate.

>
> Add two new DTS properties to set the margin between the input frequency
> and the calculated corner frequency
And this feels like a feature. So 3rd patch that we don't necessarily
backport. For earlier stages we just use the default values that
you have in the binding.

>
> Below is a generated table of the differences between the old algorithm
> and the new. This is a sweep from 0 to 20 GHz in 10 MHz steps.

So, these are just the entries where the 3db point changes?
All the others are same?

> === HPF ===
> freq = 1750 MHz, 3db: bypass => 1750 MHz
> freq = 3400 MHz, 3db: 3310 => 3400 MHz
> freq = 3410 MHz, 3db: 3310 => 3400 MHz
> freq = 3420 MHz, 3db: 3310 => 3400 MHz
> freq = 3660 MHz, 3db: 3550 => 3656 MHz
> freq = 6600 MHz, 3db: 6479 => 6600 MHz
> freq = 6610 MHz, 3db: 6479 => 6600 MHz
> freq = 6620 MHz, 3db: 6479 => 6600 MHz
> freq = 6630 MHz, 3db: 6479 => 6600 MHz
> freq = 6640 MHz, 3db: 6479 => 6600 MHz
> freq = 6650 MHz, 3db: 6479 => 6600 MHz
> freq = 6660 MHz, 3db: 6479 => 6600 MHz
> freq = 6670 MHz, 3db: 6479 => 6600 MHz
> freq = 6680 MHz, 3db: 6479 => 6600 MHz
> freq = 6690 MHz, 3db: 6479 => 6600 MHz
> freq = 6700 MHz, 3db: 6479 => 6600 MHz
> freq = 6710 MHz, 3db: 6479 => 6600 MHz
> freq = 6720 MHz, 3db: 6479 => 6600 MHz
> freq = 6730 MHz, 3db: 6479 => 6600 MHz
> freq = 6960 MHz, 3db: 6736 => 6960 MHz
> freq = 6970 MHz, 3db: 6736 => 6960 MHz
> freq = 6980 MHz, 3db: 6736 => 6960 MHz
> freq = 6990 MHz, 3db: 6736 => 6960 MHz
> freq = 7320 MHz, 3db: 7249 => 7320 MHz
> freq = 7330 MHz, 3db: 7249 => 7320 MHz
> freq = 7340 MHz, 3db: 7249 => 7320 MHz
> freq = 7350 MHz, 3db: 7249 => 7320 MHz
> freq = 7360 MHz, 3db: 7249 => 7320 MHz
> freq = 7370 MHz, 3db: 7249 => 7320 MHz
> freq = 7380 MHz, 3db: 7249 => 7320 MHz
> freq = 7390 MHz, 3db: 7249 => 7320 MHz
> freq = 7400 MHz, 3db: 7249 => 7320 MHz
> freq = 7410 MHz, 3db: 7249 => 7320 MHz
> freq = 7420 MHz, 3db: 7249 => 7320 MHz
> freq = 7430 MHz, 3db: 7249 => 7320 MHz
> freq = 7440 MHz, 3db: 7249 => 7320 MHz
> freq = 7450 MHz, 3db: 7249 => 7320 MHz
> freq = 7460 MHz, 3db: 7249 => 7320 MHz
> freq = 7470 MHz, 3db: 7249 => 7320 MHz
> freq = 7480 MHz, 3db: 7249 => 7320 MHz
> freq = 7490 MHz, 3db: 7249 => 7320 MHz
> freq = 7500 MHz, 3db: 7249 => 7320 MHz
> freq = 12500 MHz, 3db: 12000 => 12500 MHz
>
> === LPF ===
> freq = 2050 MHz, 3db: bypass => 2050 MHz
> freq = 2170 MHz, 3db: 2290 => 2170 MHz
> freq = 2290 MHz, 3db: 2410 => 2290 MHz
> freq = 2410 MHz, 3db: 2530 => 2410 MHz
> freq = 2530 MHz, 3db: 2650 => 2530 MHz
> freq = 2650 MHz, 3db: 2770 => 2650 MHz
> freq = 2770 MHz, 3db: 2890 => 2770 MHz
> freq = 2890 MHz, 3db: 3010 => 2890 MHz
> freq = 3010 MHz, 3db: 3130 => 3010 MHz
> freq = 3130 MHz, 3db: 3250 => 3130 MHz
> freq = 3250 MHz, 3db: 3370 => 3250 MHz
> freq = 3260 MHz, 3db: 3370 => 3350 MHz
> freq = 3270 MHz, 3db: 3370 => 3350 MHz
> freq = 3280 MHz, 3db: 3370 => 3350 MHz
> freq = 3290 MHz, 3db: 3370 => 3350 MHz
> freq = 3300 MHz, 3db: 3370 => 3350 MHz
> freq = 3310 MHz, 3db: 3370 => 3350 MHz
> freq = 3320 MHz, 3db: 3370 => 3350 MHz
> freq = 3330 MHz, 3db: 3370 => 3350 MHz
> freq = 3340 MHz, 3db: 3370 => 3350 MHz
> freq = 3350 MHz, 3db: 3370 => 3350 MHz
> freq = 3370 MHz, 3db: 3490 => 3370 MHz
> freq = 3490 MHz, 3db: 3610 => 3490 MHz
> freq = 3610 MHz, 3db: 3730 => 3610 MHz
> freq = 3730 MHz, 3db: 3850 => 3730 MHz
> freq = 3850 MHz, 3db: 3870 => 3850 MHz
> freq = 3870 MHz, 3db: 4130 => 3870 MHz
> freq = 4130 MHz, 3db: 4390 => 4130 MHz
> freq = 4390 MHz, 3db: 4650 => 4390 MHz
> freq = 4650 MHz, 3db: 4910 => 4650 MHz
> freq = 4910 MHz, 3db: 5170 => 4910 MHz
> freq = 5170 MHz, 3db: 5430 => 5170 MHz
> freq = 5430 MHz, 3db: 5690 => 5430 MHz
> freq = 5690 MHz, 3db: 5950 => 5690 MHz
> freq = 5950 MHz, 3db: 6210 => 5950 MHz
> freq = 6210 MHz, 3db: 6470 => 6210 MHz
> freq = 6470 MHz, 3db: 6730 => 6470 MHz
> freq = 6730 MHz, 3db: 6990 => 6730 MHz
> freq = 6990 MHz, 3db: 7250 => 6990 MHz
> freq = 7000 MHz, 3db: 7250 => 7000 MHz
> freq = 7250 MHz, 3db: 7400 => 7250 MHz
> freq = 7400 MHz, 3db: 7800 => 7400 MHz
> freq = 7800 MHz, 3db: 8200 => 7800 MHz
> freq = 8200 MHz, 3db: 8600 => 8200 MHz
> freq = 8600 MHz, 3db: 9000 => 8600 MHz
> freq = 9000 MHz, 3db: 9400 => 9000 MHz
> freq = 9400 MHz, 3db: 9800 => 9400 MHz
> freq = 9800 MHz, 3db: 10200 => 9800 MHz
> freq = 10200 MHz, 3db: 10600 => 10200 MHz
> freq = 10600 MHz, 3db: 11000 => 10600 MHz
> freq = 11000 MHz, 3db: 11400 => 11000 MHz
> freq = 11400 MHz, 3db: 11800 => 11400 MHz
> freq = 11800 MHz, 3db: 12200 => 11800 MHz
> freq = 12200 MHz, 3db: 12600 => 12200 MHz
> freq = 12210 MHz, 3db: 12600 => 12550 MHz
> freq = 12220 MHz, 3db: 12600 => 12550 MHz
> freq = 12230 MHz, 3db: 12600 => 12550 MHz
> freq = 12240 MHz, 3db: 12600 => 12550 MHz
> freq = 12250 MHz, 3db: 12600 => 12550 MHz
> freq = 12260 MHz, 3db: 12600 => 12550 MHz
> freq = 12270 MHz, 3db: 12600 => 12550 MHz
> freq = 12280 MHz, 3db: 12600 => 12550 MHz
> freq = 12290 MHz, 3db: 12600 => 12550 MHz
> freq = 12300 MHz, 3db: 12600 => 12550 MHz
> freq = 12310 MHz, 3db: 12600 => 12550 MHz
> freq = 12320 MHz, 3db: 12600 => 12550 MHz
> freq = 12330 MHz, 3db: 12600 => 12550 MHz
> freq = 12340 MHz, 3db: 12600 => 12550 MHz
> freq = 12350 MHz, 3db: 12600 => 12550 MHz
> freq = 12360 MHz, 3db: 12600 => 12550 MHz
> freq = 12370 MHz, 3db: 12600 => 12550 MHz
> freq = 12380 MHz, 3db: 12600 => 12550 MHz
> freq = 12390 MHz, 3db: 12600 => 12550 MHz
> freq = 12400 MHz, 3db: 12600 => 12550 MHz
> freq = 12410 MHz, 3db: 12600 => 12550 MHz
> freq = 12420 MHz, 3db: 12600 => 12550 MHz
> freq = 12430 MHz, 3db: 12600 => 12550 MHz
> freq = 12440 MHz, 3db: 12600 => 12550 MHz
> freq = 12450 MHz, 3db: 12600 => 12550 MHz
> freq = 12460 MHz, 3db: 12600 => 12550 MHz
> freq = 12470 MHz, 3db: 12600 => 12550 MHz
> freq = 12480 MHz, 3db: 12600 => 12550 MHz
> freq = 12490 MHz, 3db: 12600 => 12550 MHz
> freq = 12500 MHz, 3db: 12600 => 12550 MHz
> freq = 12510 MHz, 3db: 12600 => 12550 MHz
> freq = 12520 MHz, 3db: 12600 => 12550 MHz
> freq = 12530 MHz, 3db: 12600 => 12550 MHz
> freq = 12540 MHz, 3db: 12600 => 12550 MHz
> freq = 12550 MHz, 3db: 12600 => 12550 MHz
> freq = 12600 MHz, 3db: 13000 => 12600 MHz
> freq = 12610 MHz, 3db: 13000 => 12970 MHz
> freq = 12620 MHz, 3db: 13000 => 12970 MHz
> freq = 12630 MHz, 3db: 13000 => 12970 MHz
> freq = 12640 MHz, 3db: 13000 => 12970 MHz
> freq = 12650 MHz, 3db: 13000 => 12970 MHz
> freq = 12660 MHz, 3db: 13000 => 12970 MHz
> freq = 12670 MHz, 3db: 13000 => 12970 MHz
> freq = 12680 MHz, 3db: 13000 => 12970 MHz
> freq = 12690 MHz, 3db: 13000 => 12970 MHz
> freq = 12700 MHz, 3db: 13000 => 12970 MHz
> freq = 12710 MHz, 3db: 13000 => 12970 MHz
> freq = 12720 MHz, 3db: 13000 => 12970 MHz
> freq = 12730 MHz, 3db: 13000 => 12970 MHz
> freq = 12740 MHz, 3db: 13000 => 12970 MHz
> freq = 12750 MHz, 3db: 13000 => 12970 MHz
> freq = 12760 MHz, 3db: 13000 => 12970 MHz
> freq = 12770 MHz, 3db: 13000 => 12970 MHz
> freq = 12780 MHz, 3db: 13000 => 12970 MHz
> freq = 12790 MHz, 3db: 13000 => 12970 MHz
> freq = 12800 MHz, 3db: 13000 => 12970 MHz
> freq = 12810 MHz, 3db: 13000 => 12970 MHz
> freq = 12820 MHz, 3db: 13000 => 12970 MHz
> freq = 12830 MHz, 3db: 13000 => 12970 MHz
> freq = 12840 MHz, 3db: 13000 => 12970 MHz
> freq = 12850 MHz, 3db: 13000 => 12970 MHz
> freq = 12860 MHz, 3db: 13000 => 12970 MHz
> freq = 12870 MHz, 3db: 13000 => 12970 MHz
> freq = 12880 MHz, 3db: 13000 => 12970 MHz
> freq = 12890 MHz, 3db: 13000 => 12970 MHz
> freq = 12900 MHz, 3db: 13000 => 12970 MHz
> freq = 12910 MHz, 3db: 13000 => 12970 MHz
> freq = 12920 MHz, 3db: 13000 => 12970 MHz
> freq = 12930 MHz, 3db: 13000 => 12970 MHz
> freq = 12940 MHz, 3db: 13000 => 12970 MHz
> freq = 12950 MHz, 3db: 13000 => 12970 MHz
> freq = 12960 MHz, 3db: 13000 => 12970 MHz
> freq = 12970 MHz, 3db: 13000 => 12970 MHz
> freq = 13000 MHz, 3db: 13390 => 13000 MHz
> freq = 13390 MHz, 3db: 13810 => 13390 MHz
> freq = 13810 MHz, 3db: 14230 => 13810 MHz
> freq = 14230 MHz, 3db: 14650 => 14230 MHz
> freq = 14650 MHz, 3db: 15070 => 14650 MHz
> freq = 15070 MHz, 3db: 15490 => 15070 MHz
> freq = 15490 MHz, 3db: 15910 => 15490 MHz
> freq = 15910 MHz, 3db: 16330 => 15910 MHz
> freq = 16330 MHz, 3db: 16750 => 16330 MHz
> freq = 16750 MHz, 3db: 17170 => 16750 MHz
> freq = 17170 MHz, 3db: 17590 => 17170 MHz
> freq = 17590 MHz, 3db: 18010 => 17590 MHz
> freq = 18010 MHz, 3db: 18430 => 18010 MHz
> freq = 18430 MHz, 3db: 18850 => 18430 MHz
> freq = 18850 MHz, 3db: bypass => 18850 MHz
>
> Fixes: f34fe888ad05 ("iio:filter:admv8818: add support for ADMV8818")
> Signed-off-by: Sam Winchenbach <sam.winchenbach@framepointer.org>
> ---
> V1 -> V2: Cleaned up the wording of the commit message
> V2 -> V3: Add DTS properties to control corner frequency margins
> ---
> drivers/iio/filter/admv8818.c | 136 ++++++++++++++++++++++++++--------
> 1 file changed, 105 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/iio/filter/admv8818.c b/drivers/iio/filter/admv8818.c
> index 848baa6e3bbf..a446d8d421ae 100644
> --- a/drivers/iio/filter/admv8818.c
> +++ b/drivers/iio/filter/admv8818.c
> @@ -90,6 +90,8 @@ struct admv8818_state {
> struct mutex lock;
> unsigned int filter_mode;
> u64 cf_hz;
> + u64 lpf_margin_hz;
> + u64 hpf_margin_hz;
> };
>
> static const unsigned long long freq_range_hpf[4][2] = {
> @@ -103,7 +105,7 @@ static const unsigned long long freq_range_lpf[4][2] = {
> {2050000000ULL, 3850000000ULL},
> {3350000000ULL, 7250000000ULL},
> {7000000000, 13000000000},
> - {12550000000, 18500000000}
> + {12550000000, 18850000000}

As above. This seems to be the first fix and should stand on it's own.

> };
>
> static const struct regmap_config admv8818_regmap_config = {
> @@ -122,43 +124,59 @@ static const char * const admv8818_modes[] = {
> static int __admv8818_hpf_select(struct admv8818_state *st, u64 freq)
> {
> unsigned int hpf_step = 0, hpf_band = 0, i, j;
> + u64 freq_error;
> + u64 min_freq_error;
> + u64 freq_corner;
> u64 freq_step;
> int ret;
>
> if (freq < freq_range_hpf[0][0])
> goto hpf_write;
>
> - if (freq > freq_range_hpf[3][1]) {
> + if (freq >= freq_range_hpf[3][1]) {
> hpf_step = 15;
> hpf_band = 4;
>
> goto hpf_write;
> }
>
> + /* Close HPF frequency gap between 12 and 12.5 GHz */
> + if (freq >= 12000 * HZ_PER_MHZ && freq < 12500 * HZ_PER_MHZ) {
> + hpf_step = 15;
> + hpf_band = 3;
> +
> + goto hpf_write;
> + }
> +
> + min_freq_error = U64_MAX;
> for (i = 0; i < 4; i++) {

Can we get that 4 from an array size rather than hard coding here?

> + /* This (and therefore all other ranges) have a corner

Multiline comment in IIO (and most of kernel for that matter) is
/*
* This...

> + * frequency higher than the target frequency.
> + */
> + if (freq_range_hpf[i][0] > freq)
> + break;
> +
> freq_step = div_u64((freq_range_hpf[i][1] -
> freq_range_hpf[i][0]), 15);
>
> - if (freq > freq_range_hpf[i][0] &&
> - (freq < freq_range_hpf[i][1] + freq_step)) {
> - hpf_band = i + 1;
> + for (j = 0; j <= 15; j++) {

Similarly, where does the 15 come from? It's kind of in the old
code but given you are changing this good to make that clearer in
some fashion.

> + freq_corner = freq_range_hpf[i][0] + (freq_step * j);
No need for brackets around the two multiplied term.

For all these comments check for other instances. I'm just pointing out one.
> +
> + /* This (and therefore all other steps) have a corner
> + * frequency higher than the target frequency.
> + */
> + if (freq_corner > freq)
> + break;
>
> - for (j = 1; j <= 16; j++) {
> - if (freq < (freq_range_hpf[i][0] + (freq_step * j))) {
> - hpf_step = j - 1;
> - break;
> - }
> + freq_error = freq - freq_corner;
> + if (freq_error < min_freq_error) {
> + min_freq_error = freq_error;
> + hpf_step = j;
> + hpf_band = i + 1;
> }
> - break;
> }
> }
>
> - /* Close HPF frequency gap between 12 and 12.5 GHz */
> - if (freq >= 12000 * HZ_PER_MHZ && freq <= 12500 * HZ_PER_MHZ) {
> - hpf_band = 3;
> - hpf_step = 15;
> - }
> -
> hpf_write:
> ret = regmap_update_bits(st->regmap, ADMV8818_REG_WR0_SW,
> ADMV8818_SW_IN_SET_WR0_MSK |
> @@ -186,7 +204,11 @@ static int admv8818_hpf_select(struct admv8818_state *st, u64 freq)
>
> static int __admv8818_lpf_select(struct admv8818_state *st, u64 freq)
> {
> - unsigned int lpf_step = 0, lpf_band = 0, i, j;
> + int i, j;

Might as well combine with declaration of ret below.

> + unsigned int lpf_step = 0, lpf_band = 0;
> + u64 freq_error;
> + u64 min_freq_error;
> + u64 freq_corner;
Good to combine a few of these related u64 as single line declaration..

> u64 freq_step;
> int ret;
>
> @@ -199,18 +221,34 @@ static int __admv8818_lpf_select(struct admv8818_state *st, u64 freq)
> goto lpf_write;
> }
>
> - for (i = 0; i < 4; i++) {
> - if (freq > freq_range_lpf[i][0] && freq < freq_range_lpf[i][1]) {
> - lpf_band = i + 1;
> - freq_step = div_u64((freq_range_lpf[i][1] - freq_range_lpf[i][0]), 15);
> -
> - for (j = 0; j <= 15; j++) {
> - if (freq < (freq_range_lpf[i][0] + (freq_step * j))) {
> - lpf_step = j;
> - break;
> - }
> - }
> + min_freq_error = U64_MAX;
> + for (i = 3; i >= 0; --i) {

As above. If that 3 comes from an array size, please make that clear.

> + /* At this point the highest corner frequency of
> + * all remaining ranges is below the target.
> + * LPF corner should be >= the target.
> + */
> + if (freq > freq_range_lpf[i][1])
> break;
> +
> + freq_step = div_u64((freq_range_lpf[i][1] - freq_range_lpf[i][0]), 15);
> +
> + for (j = 15; j >= 0; --j) {
> +
> + freq_corner = freq_range_lpf[i][0] + j*freq_step;
> +
> + /* At this point all other steps in range will
> + * place the corner frequency below the target
> + * LPF corner should >= the target.
> + */
> + if (freq > freq_corner)
> + break;
> +
> + freq_error = freq_corner - freq;
> + if (freq_error < min_freq_error) {
> + min_freq_error = freq_error;
> + lpf_step = j;
> + lpf_band = i + 1;
> + }
> }
> }
>
> @@ -242,16 +280,28 @@ static int admv8818_lpf_select(struct admv8818_state *st, u64 freq)
> static int admv8818_rfin_band_select(struct admv8818_state *st)
> {
> int ret;
> + u64 hpf_corner_target, lpf_corner_target;
>
> st->cf_hz = clk_get_rate(st->clkin);
>
> + // Check for underflow

No C++ style comments in IIO code. This is just a consistency thing rather than
really matter. We have lots of code that predates those being at all acceptable
in the kernel and a mixture of the two styles is messy!

> + if (st->cf_hz > st->hpf_margin_hz)
> + hpf_corner_target = st->cf_hz - st->hpf_margin_hz;
> + else
> + hpf_corner_target = 0;
> +
> + // Check for overflow
> + lpf_corner_target = st->cf_hz + st->lpf_margin_hz;
> + if (lpf_corner_target < st->cf_hz)
> + lpf_corner_target = U64_MAX;
> +
> mutex_lock(&st->lock);
>
> - ret = __admv8818_hpf_select(st, st->cf_hz);
> + ret = __admv8818_hpf_select(st, hpf_corner_target);
> if (ret)
> goto exit;
>
> - ret = __admv8818_lpf_select(st, st->cf_hz);
> + ret = __admv8818_lpf_select(st, lfp_corner_target);
> exit:
> mutex_unlock(&st->lock);
> return ret;
> @@ -647,6 +697,26 @@ static int admv8818_clk_setup(struct admv8818_state *st)
> return devm_add_action_or_reset(&spi->dev, admv8818_clk_notifier_unreg, st);
> }
>
> +static int admv8818_read_properties(struct admv8818_state *st)
> +{
> + struct spi_device *spi = st->spi;
> + int ret;
> +
> + ret = device_property_read_u64(&spi->dev, "adi,lpf-margin-hz", &st->lpf_margin_hz);
> + if (ret == -EINVAL)
> + st->lpf_margin_hz = 0;
> + else if (ret < 0)
> + return ret;
Often for properties with defaults we don't worry too much about checking for errors other
than 'not there'. So I'd be fine with this being the simpler.

st->lpf_margin_hz = 0;
device_property_read_u64(...)

and no explicit error checking.

If you really want to retain the protection against wrong formats etc, then fair enough.
> +
> + ret = device_property_read_u64(&spi->dev, "adi,hpf-margin-hz", &st->hpf_margin_hz);
> + if (ret == -EINVAL)
> + st->hpf_margin_hz = 0;
> + else if (ret < 0)
> + return ret;
> +
> + return 0;
> +}
> +
> static int admv8818_probe(struct spi_device *spi)
> {
> struct iio_dev *indio_dev;
> @@ -678,6 +748,10 @@ static int admv8818_probe(struct spi_device *spi)
>
> mutex_init(&st->lock);
>
> + ret = admv8818_read_properties(st);
I haven't checked but if this is first place that you use property.h then
need that included.

> + if (ret)
> + return ret;
> +
> ret = admv8818_init(st);
> if (ret)
> return ret;