• Geert Uytterhoeven's avatar
    iio: adc: max9611: Fix too short conversion time delay · 9fd229c4
    Geert Uytterhoeven authored
    As of commit b9ddd509 ("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: 69780a3b ("iio: adc: Add Maxim max9611 ADC driver")
    Signed-off-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
    Reviewed-by: default avatarJacopo Mondi <jacopo+renesas@jmondi.org>
    Reviewed-by: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
    Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
    9fd229c4
max9611.c 14.7 KB