From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:35830 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751706AbdGHNMA (ORCPT ); Sat, 8 Jul 2017 09:12:00 -0400 From: Hans de Goede To: Jonathan Cameron Cc: Hans de Goede , Lars-Peter Clausen , Peter Meerwald-Stadler , linux-iio@vger.kernel.org Subject: [PATCH] iio: adc: axp288: Fix the GPADC pin reading often wrongly returning 0 Date: Sat, 8 Jul 2017 15:11:57 +0200 Message-Id: <20170708131157.13704-1-hdegoede@redhat.com> Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org 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 --- 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, -- 2.13.0