Hi Geert,
On Wed, Nov 13, 2019 at 10:21:33AM +0100, Geert Uytterhoeven wrote:
> 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. 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 2000-2200 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@xxxxxxxxx>
> ---
> This problem was exposed in v5.3.
>
> After this patch, probing of the two max9611 sensors succeeded during
> ca. 3000 boot cycles on Salvator-X(S) boards, equipped with various
> R-Car H3/M3-W/M3-N SoCs.
> ---
> drivers/iio/adc/max9611.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/adc/max9611.c b/drivers/iio/adc/max9611.c
> index da073d72f649f829..b0755f25356d700d 100644
> --- a/drivers/iio/adc/max9611.c
> +++ b/drivers/iio/adc/max9611.c
> @@ -89,6 +89,11 @@
> #define MAX9611_TEMP_SCALE_NUM 1000000
> #define MAX9611_TEMP_SCALE_DIV 2083
>
> +/*
> + * Conversion time is 2 ms (typically)
> + */
> +#define MAX9611_CONV_TIME_US_RANGE 2000, 2200
> +
Is a 20% sleep range enough or should it be slightly lengthen ?
Apart from this, thanks a lot for finding the issue root cause!
Reviewed-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
Thanks
j
> struct max9611_dev {
> struct device *dev;
> struct i2c_client *i2c_client;
> @@ -238,9 +243,9 @@ static int max9611_read_single(struct max9611_dev *max9611,
>
> /*
> * need a delay here to make register configuration
> - * stabilize. 1 msec at least, from empirical testing.
> + * stabilize.
> */
> - usleep_range(1000, 2000);
> + usleep_range(MAX9611_CONV_TIME_US_RANGE);
>
> ret = i2c_smbus_read_word_swapped(max9611->i2c_client, reg_addr);
> if (ret < 0) {
> @@ -507,7 +512,7 @@ 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;
> }
> --
> 2.17.1
>
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