From: Geert Uytterhoeven geert+renesas@glider.be
[ Upstream commit 9fd229c478fbf77c41c8528aa757ef14210365f6 ]
As of commit b9ddd5091160793e ("iio: adc: max9611: Fix temperature reading in probe"), max9611 initialization sometimes fails on the Salvator-X(S) development board with:
max9611 4-007f: Invalid value received from ADC 0x8000: aborting max9611: probe of 4-007f failed with error -5
The max9611 driver tests communications with the chip by reading the die temperature during the probe function, which returns an invalid value.
According to the datasheet, the typical ADC conversion time is 2 ms, but no minimum or maximum values are provided. Maxim Technical Support confirmed this was tested with temperature Ta=25 degreeC, and promised to inform me if a maximum/minimum value is available (they didn't get back to me, so I assume it is not).
However, the driver assumes a 1 ms conversion time. Usually the usleep_range() call returns after more than 1.8 ms, hence it succeeds. When it returns earlier, the data register may be read too early, and the previous measurement value will be returned. After boot, this is the temperature POR (power-on reset) value, causing the failure above.
Fix this by increasing the delay from 1000-2000 µs to 3000-3300 µs.
Note that this issue has always been present, but it was exposed by the aformentioned commit.
Fixes: 69780a3bbc0b1e7e ("iio: adc: Add Maxim max9611 ADC driver") Signed-off-by: Geert Uytterhoeven geert+renesas@glider.be Reviewed-by: Jacopo Mondi jacopo+renesas@jmondi.org Reviewed-by: Wolfram Sang wsa+renesas@sang-engineering.com Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/iio/adc/max9611.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/drivers/iio/adc/max9611.c b/drivers/iio/adc/max9611.c index 33be07c78b96..8649a61c50bc 100644 --- a/drivers/iio/adc/max9611.c +++ b/drivers/iio/adc/max9611.c @@ -92,6 +92,12 @@ #define MAX9611_TEMP_SCALE_NUM 1000000 #define MAX9611_TEMP_SCALE_DIV 2083
+/* + * Conversion time is 2 ms (typically) at Ta=25 degreeC + * No maximum value is known, so play it safe. + */ +#define MAX9611_CONV_TIME_US_RANGE 3000, 3300 + struct max9611_dev { struct device *dev; struct i2c_client *i2c_client; @@ -239,11 +245,9 @@ static int max9611_read_single(struct max9611_dev *max9611, return ret; }
- /* - * need a delay here to make register configuration - * stabilize. 1 msec at least, from empirical testing. - */ - usleep_range(1000, 2000); + /* need a delay here to make register configuration stabilize. */ + + usleep_range(MAX9611_CONV_TIME_US_RANGE);
ret = i2c_smbus_read_word_swapped(max9611->i2c_client, reg_addr); if (ret < 0) { @@ -511,7 +515,7 @@ static int max9611_init(struct max9611_dev *max9611) MAX9611_REG_CTRL2, 0); return ret; } - usleep_range(1000, 2000); + usleep_range(MAX9611_CONV_TIME_US_RANGE);
return 0; }