On Mon, Dec 02, 2019 at 09:55:46AM +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. 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 > Reviewed-by: Jacopo Mondi Reviewed-by: Wolfram Sang One minor nit, though: > /* > * need a delay here to make register configuration > - * stabilize. 1 msec at least, from empirical testing. > + * stabilize. This could be a one line comment now?