iio: adc: stm32-dfsdm: fix successive oversampling settings

When doing successive oversampling settings, it may fail to update filter
parameters silently:
- First time oversampling is being set, it will be successful, as fl->res
is 0 initially.
- Next attempts with various oversamp value may return 0 (success), but
keep previous filter parameters, due to 'res' never reaches above or
equal current 'fl->res'.

This is particularly true when setting sampling frequency (that relies on
oversamp). Typical failure without error:
- run 1st test @16kHz samp freq will succeed
- run new test @8kHz will succeed as well
- run new test @16kHz (again): sample rate will remain 8kHz without error

Fixes: e2e6771c6462 ("IIO: ADC: add STM32 DFSDM sigma delta ADC support")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index 01422d11753cf39be105b9352e06746927d75731..dc911b6fedd6750f29a14b3c3540c75016e1e757 100644 (file)
--- a/drivers/iio/adc/stm32-dfsdm-adc.c
+++ b/drivers/iio/adc/stm32-dfsdm-adc.c
@@ -144,6 +144,7 @@ static int stm32_dfsdm_set_osrs(struct stm32_dfsdm_filter *fl,
         * Leave as soon as if exact resolution if reached.
         * Otherwise the higher resolution below 32 bits is kept.
         */
+       fl->res = 0;
        for (fosr = 1; fosr <= DFSDM_MAX_FL_OVERSAMPLING; fosr++) {
                for (iosr = 1; iosr <= DFSDM_MAX_INT_OVERSAMPLING; iosr++) {
                        if (fast)
@@ -193,7 +194,7 @@ static int stm32_dfsdm_set_osrs(struct stm32_dfsdm_filter *fl,
                }
        }
 
-       if (!fl->fosr)
+       if (!fl->res)
                return -EINVAL;
 
        return 0;