From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932301AbcHDE7F (ORCPT ); Thu, 4 Aug 2016 00:59:05 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36669 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751434AbcHDE7D (ORCPT ); Thu, 4 Aug 2016 00:59:03 -0400 MIME-Version: 1.0 In-Reply-To: <20160804033253.GA31586@d830.WORKGROUP> References: <20160804033253.GA31586@d830.WORKGROUP> From: Matt Ranostay Date: Wed, 3 Aug 2016 21:58:15 -0700 Message-ID: Subject: Re: [PATCH] iio: humidity: hdc100x: use i2c_master_recv to read sensor data To: Alison Schofield Cc: Jonathan Cameron , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , "linux-iio@vger.kernel.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 3, 2016 at 8:33 PM, Alison Schofield wrote: > Replace the i2c_smbus_read_byte commmands used to retrieve the sensor > data with an i2c_master_recv command. > > The smbus read byte method fails because the device does not expect a > stop condition after sending the first byte. When we issue the second > read, we are getting the first byte again. Net effect is that of the 14 > bits used for the measurement, the 8 most significant bits are correct, > the lower 6 are not. > > None of the smbus read protocols follow the pattern this device requires > (S Addr Rd [A] Data [A] Data NA P), hence the switch to an i2c receive > transaction. > > Signed-off-by: Alison Schofield > Cc: Daniel Baluta > --- > drivers/iio/humidity/hdc100x.c | 27 +++++++-------------------- > 1 file changed, 7 insertions(+), 20 deletions(-) > > diff --git a/drivers/iio/humidity/hdc100x.c b/drivers/iio/humidity/hdc100x.c > index a03832a..643a42d 100644 > --- a/drivers/iio/humidity/hdc100x.c > +++ b/drivers/iio/humidity/hdc100x.c > @@ -142,7 +142,7 @@ static int hdc100x_get_measurement(struct hdc100x_data *data, > struct i2c_client *client = data->client; > int delay = data->adc_int_us[chan->address]; > int ret; > - int val; > + u8 buf[2]; > > /* start measurement */ > ret = i2c_smbus_write_byte(client, chan->address); > @@ -154,26 +154,13 @@ static int hdc100x_get_measurement(struct hdc100x_data *data, > /* wait for integration time to pass */ > usleep_range(delay, delay + 1000); > > - /* > - * i2c_smbus_read_word_data cannot() be used here due to the command > - * value not being understood and causes NAKs preventing any reading > - * from being accessed. > - */ > - ret = i2c_smbus_read_byte(client); > + /* read the 2 byte measurement */ > + ret = i2c_master_recv(data->client, buf, 2); > if (ret < 0) { > - dev_err(&client->dev, "cannot read high byte measurement"); > + dev_err(&client->dev, "cannot read sensor data\n"); > return ret; > } > - val = ret << 8; > - > - ret = i2c_smbus_read_byte(client); > - if (ret < 0) { > - dev_err(&client->dev, "cannot read low byte measurement"); > - return ret; > - } > - val |= ret; > - > - return val; > + return (int)(buf[0] << 8 | buf[1]); Pretty sure you don't need to cast to int type here. > } > > static int hdc100x_get_heater_status(struct hdc100x_data *data) > @@ -272,8 +259,8 @@ static int hdc100x_probe(struct i2c_client *client, > struct iio_dev *indio_dev; > struct hdc100x_data *data; > > - if (!i2c_check_functionality(client->adapter, > - I2C_FUNC_SMBUS_WORD_DATA | I2C_FUNC_SMBUS_BYTE)) > + if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA | > + I2C_FUNC_SMBUS_BYTE | I2C_FUNC_I2C)) Not sure we want to kill smbus support for this device... iwe should have two read methods for i2c and smbus (see the PulsedLight LIDAR driver) in this case. Ideally I wouldn't have written it with only smbus in mind, but can kill backwards compatibility unless we have a good reason. Thanks, Matt > return -EOPNOTSUPP; > > indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data)); > -- > 2.1.4 >