From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752512AbeCUOag (ORCPT ); Wed, 21 Mar 2018 10:30:36 -0400 Received: from mail-qk0-f195.google.com ([209.85.220.195]:43324 "EHLO mail-qk0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752447AbeCUOa3 (ORCPT ); Wed, 21 Mar 2018 10:30:29 -0400 X-Google-Smtp-Source: AIpwx4+0nXPwVKIYntoAvrV+1XhtRNgw40tlK6cw0DD3uSznN9Q2TBGvhWAM5uVnKixCg5MmEmakWQ== From: =?UTF-8?q?Hern=C3=A1n=20Gonzalez?= To: lars@metafoo.de, Michael.Hennerich@analog.com, jic23@kernel.org, knaack.h@gmx.de, pmeerw@pmeerw.net, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, hernan@vanguardiasur.com.ar Subject: [PATCH 08/11] staging: iio: ad7746: Add comments Date: Wed, 21 Mar 2018 11:28:56 -0300 Message-Id: <1521642539-4845-9-git-send-email-hernan@vanguardiasur.com.ar> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1521642539-4845-1-git-send-email-hernan@vanguardiasur.com.ar> References: <1521642539-4845-1-git-send-email-hernan@vanguardiasur.com.ar> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add comments to clarify some of the calculations made, specially when reading or writing values. Signed-off-by: Hernán Gonzalez --- drivers/staging/iio/cdc/ad7746.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-) diff --git a/drivers/staging/iio/cdc/ad7746.c b/drivers/staging/iio/cdc/ad7746.c index 8abba71..b6b99e2 100644 --- a/drivers/staging/iio/cdc/ad7746.c +++ b/drivers/staging/iio/cdc/ad7746.c @@ -420,6 +420,7 @@ static int ad7746_write_raw(struct iio_dev *indio_dev, goto out; } + /* 2^16 in micro */ val = (val2 * 1024) / 15625; switch (chan->type) { @@ -546,6 +547,13 @@ static int ad7746_read_raw(struct iio_dev *indio_dev, if (ret < 0) goto out; + /* + * Either for Capacitance, Voltage or Temperature, + * the 0x000000 code represents negative full scale, + * the 0x800000 code represents zero scale, and + * the 0xFFFFFF code represents positive full scale. + */ + *val = (be32_to_cpu(chip->data.d32) & 0xFFFFFF) - 0x800000; switch (chan->type) { @@ -557,7 +565,13 @@ static int ad7746_read_raw(struct iio_dev *indio_dev, *val = (*val * 125) / 256; break; case IIO_VOLTAGE: - if (chan->channel == 1) /* supply_raw*/ + + /* + * The voltage from the VDD pin is internally + * attenuated by 6. + */ + + if (chan->channel == 1) /* supply_raw */ *val = *val * 6; break; default: @@ -598,21 +612,28 @@ static int ad7746_read_raw(struct iio_dev *indio_dev, ret = IIO_VAL_INT; break; case IIO_CHAN_INFO_OFFSET: + + /* + * CAPDAC Scale = 21pF_typ / 127 + * CIN Scale = 8.192pF / 2^24 + * Offset Scale = CAPDAC Scale / CIN Scale = 338646 + */ + *val = AD7746_CAPDAC_DACP(chip->capdac[chan->channel] - [chan->differential]) * 338646; + [chan->differential]) * 338646; ret = IIO_VAL_INT; break; case IIO_CHAN_INFO_SCALE: switch (chan->type) { case IIO_CAPACITANCE: - /* 8.192pf / 2^24 */ + /* CIN Scale: 8.192pf / 2^24 */ *val = 0; *val2 = 488; ret = IIO_VAL_INT_PLUS_NANO; break; case IIO_VOLTAGE: - /* 1170mV / 2^23 */ + /* VIN Scale: 1170mV / 2^23 */ *val = 1170; *val2 = 23; ret = IIO_VAL_FRACTIONAL_LOG2; @@ -666,7 +687,8 @@ static struct ad7746_platform_data *ad7746_parse_dt(struct device *dev) unsigned int tmp; int ret; - /* The default excitation outputs are not inverted, it should be stated + /* + * The default excitation outputs are not inverted, it should be stated * in the dt if needed. */ @@ -678,7 +700,7 @@ static struct ad7746_platform_data *ad7746_parse_dt(struct device *dev) ret = of_property_read_u32(np, "adi,exclvl", &tmp); if (ret || tmp > 3) { dev_warn(dev, "Wrong exclvl value, using default\n"); - pdata->exclvl = 3; /* default value */ + pdata->exclvl = 3; } else { pdata->exclvl = tmp; } -- 2.7.4