On Sat, 8 Jul 2017 15:11:57 +0200
Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> I noticed in its DSDT that one of my tablets actually is using the GPADC
> pin for temperature monitoring.
>
> The whole axp288_adc_set_ts() function is a bit weird, in the past it was
> removed because it seems to make no sense, then this was reverted because
> of regressions.
>
> So I decided to test the special GPADC pin handling on this tablet.
> Conclusion: not only is axp288_adc_set_ts() necessary, we need to sleep a
> bit after making the AXP288_ADC_TS_PIN_CTRL changes before sampling the
> GPADC, otherwise it will often (about 80% of the time) read 0 instead of
> its actual value.
>
> It seems that there is only 1 bias current source and to be able to use it
> for the GPIO0 pin in GPADC mode it must be temporarily turned off for the
> TS pin, but the datasheet does not mention this.
>
> This commit adds a sleep after disabling the TS pin bias current,
> fixing the GPADC more often then not wrongly returning 0.
>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Hans,
This is sufficiently weird that I want your opinion on what
to do with this. Are we looking at a necessary fix for a hardware
platform that we should push out asap and mark for stable?
Or is this a bit of an odd corner case where a slower path makes
more sense?
I'm happy either way.
Jonathan
> ---
> drivers/iio/adc/axp288_adc.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iio/adc/axp288_adc.c b/drivers/iio/adc/axp288_adc.c
> index 7fd24949c0c1..462a99c13e7a 100644
> --- a/drivers/iio/adc/axp288_adc.c
> +++ b/drivers/iio/adc/axp288_adc.c
> @@ -126,11 +126,21 @@ static int axp288_adc_read_channel(int *val, unsigned long address,
> static int axp288_adc_set_ts(struct regmap *regmap, unsigned int mode,
> unsigned long address)
> {
> + int ret;
> +
> /* channels other than GPADC do not need to switch TS pin */
> if (address != AXP288_GP_ADC_H)
> return 0;
>
> - return regmap_write(regmap, AXP288_ADC_TS_PIN_CTRL, mode);
> + ret = regmap_write(regmap, AXP288_ADC_TS_PIN_CTRL, mode);
> + if (ret)
> + return ret;
> +
> + /* When switching to the GPADC pin give things some time to settle */
> + if (mode == AXP288_ADC_TS_PIN_GPADC)
> + usleep_range(6000, 10000);
> +
> + return 0;
> }
>
> static int axp288_adc_read_raw(struct iio_dev *indio_dev,
--
To unsubscribe from this list: send the line "unsubscribe linux-iio" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
