From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763094AbdAIRKC (ORCPT ); Mon, 9 Jan 2017 12:10:02 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:45851 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763057AbdAIRJy (ORCPT ); Mon, 9 Jan 2017 12:09:54 -0500 Date: Mon, 9 Jan 2017 09:09:52 -0800 From: Guenter Roeck To: jeroen.de_wachter.ext@nokia.com Cc: jdelvare@suse.com, linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] hwmon/tmp401: use smb word operations instead of 2 smb byte operations Message-ID: <20170109170952.GB16253@roeck-us.net> References: <1483980458-28202-1-git-send-email-jeroen.de_wachter.ext@nokia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1483980458-28202-1-git-send-email-jeroen.de_wachter.ext@nokia.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: guenter@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: guenter@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 09, 2017 at 05:47:37PM +0100, jeroen.de_wachter.ext@nokia.com wrote: > From: Jeroen De Wachter > > tmp401 separately read/wrote high and low bytes of temperature values while > the hardware supports reading/writing those values in one operation. Driver > has been modified to use word operations where possible. > > Tested with a tmp432 sensor on a mips64 platform. > > Signed-off-by: Jeroen De Wachter > --- > drivers/hwmon/tmp401.c | 48 +++++++++++++++++++++++++++++------------------- > 1 file changed, 29 insertions(+), 19 deletions(-) > > diff --git a/drivers/hwmon/tmp401.c b/drivers/hwmon/tmp401.c > index eeeed2c..88b17e4 100644 > --- a/drivers/hwmon/tmp401.c > +++ b/drivers/hwmon/tmp401.c > @@ -213,25 +213,29 @@ static int tmp401_update_device_reg16(struct i2c_client *client, > for (i = 0; i < num_sensors; i++) { /* local / r1 / r2 */ > for (j = 0; j < num_regs; j++) { /* temp / low / ... */ > u8 regaddr; > - /* > - * High byte must be read first immediately followed > - * by the low byte > - */ > + > regaddr = data->kind == tmp432 ? > TMP432_TEMP_MSB_READ[j][i] : > TMP401_TEMP_MSB_READ[j][i]; > - val = i2c_smbus_read_byte_data(client, regaddr); > - if (val < 0) > - return val; > - data->temp[j][i] = val << 8; > - if (j == 3) /* crit is msb only */ > - continue; > - regaddr = data->kind == tmp432 ? TMP432_TEMP_LSB[j][i] > - : TMP401_TEMP_LSB[j][i]; > - val = i2c_smbus_read_byte_data(client, regaddr); > + if (j == 3) { /* crit is msb only */ > + val = i2c_smbus_read_byte_data(client, regaddr); > + } else { > + /* > + * Hardware provides big endian data. However, > + * the smbus protocol expects the LSB first in > + * I2C_SMBUS_WORD_DATA operations. > + * i2c_smbus_read_word_swapped swaps the bytes > + * in the value it receives from > + * i2c_smbus_read_word_data before returning the > + * data, so we get the correct value. > + */ Please drop the comment or make it shorter (such as "Hardware provides big endian data"). > + val = i2c_smbus_read_word_swapped(client, > + regaddr); > + } > if (val < 0) > return val; > - data->temp[j][i] |= val; > + > + data->temp[j][i] = j == 3 ? val << 8 : val; > } > } > return 0; > @@ -373,11 +377,17 @@ static ssize_t store_temp(struct device *dev, struct device_attribute *devattr, > > regaddr = data->kind == tmp432 ? TMP432_TEMP_MSB_WRITE[nr][index] > : TMP401_TEMP_MSB_WRITE[nr][index]; > - i2c_smbus_write_byte_data(client, regaddr, reg >> 8); > - if (nr != 3) { > - regaddr = data->kind == tmp432 ? TMP432_TEMP_LSB[nr][index] > - : TMP401_TEMP_LSB[nr][index]; > - i2c_smbus_write_byte_data(client, regaddr, reg & 0xFF); > + if (nr == 3) { /* crit is msb only */ > + i2c_smbus_write_byte_data(client, regaddr, reg >> 8); > + } else { > + /* > + * Hardware expects big endian data. However, the smbus protocol > + * puts the LSB first in I2C_SMBUS_WORD_DATA operations. > + * i2c_smbus_write_word_data_swapped will swap the bytes before > + * passing them to i2c_smbus_write_word_data, so the hardware > + * will receive the MSB first, as expected. Comment in one place is enough. Unless I am missing something, TMP432_TEMP_LSB and TMP401_TEMP_LSB are now unused and can be removed. Thanks, Guenter > + */ > + i2c_smbus_write_word_swapped(client, regaddr, reg); > } > data->temp[nr][index] = reg; > > -- > 1.8.3.1 >