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From 8188c4d5deda1d747801bfafb750fd61d0292ba5 Mon Sep 17 00:00:00 2001
From: Zhikui Ren <zhikui.ren@intel.com>
Date: Tue, 13 Oct 2020 12:23:29 -0700
Subject: [PATCH] Filter erroneous adc readings
There has been cases that ast2500 ADC appears to return an incorrect
reading. Re-read the ADC data once if the ADC valuse jumped more than
80 counts comparing the previous value.
This is a workaround to filter out these erroneous readings recorded
from user space application polling every second:
PVNN_PCH_AUX history dump:
0.9,0.9,0.9,0.9,1.351,0.9,0.9,0.9,0.901,0.898
PVDQ_DEF_CPU1 history dump:
1.235,1.237,1.237,1.235,1.348,1.237,1.237,1.235,1.237,1.235
ADC raw reading is 1000 times above numbers.
This approach works if there is a silicon bug in adc register read
with minimal risk. It will not work if the bad readings come from noise
in the sensing circuitry. This patch may be removed if that is proven
to be the case.
Tested:
Build and verified no regression in voltage reading on my WC.
Signed-off-by: Zhikui Ren <zhikui.ren@intel.com>
---
drivers/iio/adc/aspeed_adc.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
index c115797c4cc5..c1e775e764ca 100644
--- a/drivers/iio/adc/aspeed_adc.c
+++ b/drivers/iio/adc/aspeed_adc.c
@@ -55,6 +55,7 @@
#define ASPEED_ADC_CHANNELS_MAX 16
#define ASPEED_ADC_RAW_VALUE_MAX 0x3ff
+#define ASPEED_ADC_RAW_VALUE_DELTA_THRESHOLD 80
struct aspeed_adc_model_data {
const char *model_name;
@@ -133,6 +134,13 @@ static int aspeed_adc_read_raw(struct iio_dev *indio_dev,
pr_err("aspeed_adc: channel %d drop invalid raw reading 0x3FF %d\n",
chan->channel, ASPEED_ADC_RAW_VALUE_MAX);
} else {
+ if (*val > (data->channel_raw_value[chan->channel] +
+ ASPEED_ADC_RAW_VALUE_DELTA_THRESHOLD)) {
+ pr_err("aspeed_adc: Warning-channel %d prev=%d, curr=%d, retry.\n",
+ chan->channel,
+ data->channel_raw_value[chan->channel], *val);
+ *val = readw(data->base + chan->address);
+ }
data->channel_raw_value[chan->channel] = *val;
}
return IIO_VAL_INT;
--
2.17.1
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