From 33d7ecbf69aa7dd4145e3b77962bcb8759eede3d Mon Sep 17 00:00:00 2001 From: Michael Hennerich Date: Fri, 29 Aug 2025 12:25:42 +0100 Subject: [PATCH] iio: frequency: adf4350: Fix prescaler usage. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The ADF4350/1 features a programmable dual-modulus prescaler of 4/5 or 8/9. When set to 4/5, the maximum RF frequency allowed is 3 GHz. Therefore, when operating the ADF4351 above 3 GHz, this must be set to 8/9. In this context not the RF output frequency is meant - it's the VCO frequency. Therefore move the prescaler selection after we derived the VCO frequency from the desired RF output frequency. This BUG may have caused PLL lock instabilities when operating the VCO at the very high range close to 4.4 GHz. Fixes: e31166f0fd48 ("iio: frequency: New driver for Analog Devices ADF4350/ADF4351 Wideband Synthesizers") Signed-off-by: Michael Hennerich Signed-off-by: Nuno Sá Reviewed-by: Andy Shevchenko Link: https://patch.msgid.link/20250829-adf4350-fix-v2-1-0bf543ba797d@analog.com Cc: Signed-off-by: Jonathan Cameron --- drivers/iio/frequency/adf4350.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/drivers/iio/frequency/adf4350.c b/drivers/iio/frequency/adf4350.c index 47f1c7e9efa9f..475a7a653bfb5 100644 --- a/drivers/iio/frequency/adf4350.c +++ b/drivers/iio/frequency/adf4350.c @@ -149,6 +149,19 @@ static int adf4350_set_freq(struct adf4350_state *st, unsigned long long freq) if (freq > ADF4350_MAX_OUT_FREQ || freq < st->min_out_freq) return -EINVAL; + st->r4_rf_div_sel = 0; + + /* + * !\TODO: The below computation is making sure we get a power of 2 + * shift (st->r4_rf_div_sel) so that freq becomes higher or equal to + * ADF4350_MIN_VCO_FREQ. This might be simplified with fls()/fls_long() + * and friends. + */ + while (freq < ADF4350_MIN_VCO_FREQ) { + freq <<= 1; + st->r4_rf_div_sel++; + } + if (freq > ADF4350_MAX_FREQ_45_PRESC) { prescaler = ADF4350_REG1_PRESCALER; mdiv = 75; @@ -157,13 +170,6 @@ static int adf4350_set_freq(struct adf4350_state *st, unsigned long long freq) mdiv = 23; } - st->r4_rf_div_sel = 0; - - while (freq < ADF4350_MIN_VCO_FREQ) { - freq <<= 1; - st->r4_rf_div_sel++; - } - /* * Allow a predefined reference division factor * if not set, compute our own -- 2.47.3