Date:	Wed, 19 Dec 2007 16:35:24 +0100
From:	Jean Delvare <khali@...ux-fr.org>
To:	Steve Hardy <steve@...uxrealtime.co.uk>
Cc:	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] : hwmon - new chip driver for TI ADS7828  A-D

Hi Steve,

On Mon, 03 Dec 2007 17:59:59 +0000, Steve Hardy wrote:
> Here is a patch against 2.6.23.9 which adds support for the 
> Burr-Brown/Texas-Instruments
> ADS7828 12-bit 8-channel A-D converter.
> 
> The chip is used for voltage monitoring on the COTS processor card I am
> currently working with.
> 
> The driver simply outputs the current input voltages (in mv as specified
> in the lm-sensors sysfs interface documentation).  Any scaling required for
> a specific board is handled by user-space.  Hopefully this makes the driver
> generic enough to be generally useful.
> 
> The driver is basically a simple rehash of existing code - I used lm75 as
> the starting point, with some inspiration from other existing drivers.
> 
> Please let me know if there are any problems with the patch.

Preliminary note: if the chip is on an embedded platform where you can
declare the devices as platform data, writing a new-style I2C driver
would probably be easier. This would save you the detection step (which
I am not sure is very reliable) and device configuration would also be
much easier.

I have some random comments on top of what Andrew already wrote:

> diff -uprN -X linux-2.6.23.9/Documentation/dontdiff 
> linux-2.6.23.9/drivers/hwmon/Kconfig 
> linux-2.6.23.9-ads7828/drivers/hwmon/Kconfig
> --- linux-2.6.23.9/drivers/hwmon/Kconfig    2007-11-26 
> 17:51:43.000000000 +0000
> +++ linux-2.6.23.9-ads7828/drivers/hwmon/Kconfig    2007-11-28 
> 10:02:02.000000000 +0000
> @@ -530,6 +530,16 @@ config SENSORS_THMC50
>        This driver can also be built as a module.  If so, the module
>        will be called thmc50.
>  
> +config SENSORS_ADS7828
> +    tristate "Texas Instruments ADS7828"
> +    depends on I2C && EXPERIMENTAL
> +    help
> +      If you say yes here you get support for Texas Instruments ADS7828
> +      12-bit 8-channel ADC device

Missing final dot.

> +
> +      This driver can also be built as a module.  If so, the module
> +      will be called ads7828

Ditto.

> +
>  config SENSORS_VIA686A
>      tristate "VIA686A"
>      depends on PCI

> diff -uprN -X linux-2.6.23.9/Documentation/dontdiff 
> linux-2.6.23.9/drivers/hwmon/ads7828.c 
> linux-2.6.23.9-ads7828/drivers/hwmon/ads7828.c
> --- linux-2.6.23.9/drivers/hwmon/ads7828.c    1970-01-01 
> 01:00:00.000000000 +0100
> +++ linux-2.6.23.9-ads7828/drivers/hwmon/ads7828.c    2007-11-28 
> 10:02:02.000000000 +0000
> @@ -0,0 +1,304 @@
> +/*
> +    ads7828.c - lm_sensors driver for ads7828 12bit 8ch ADC
> +    (C) 2007 EADS Astrium
> +
> +    This driver is based on the lm75 and other lm_sensors/hwmon drivers
> +
> +    Written by Steve Hardy <steve@...uxrealtime.co.uk>
> +
> +    Datasheet available at : http://focus.ti.com/lit/ds/symlink/ads7828.pdf
> +
> +    This program is free software; you can redistribute it and/or modify
> +    it under the terms of the GNU General Public License as published by
> +    the Free Software Foundation; either version 2 of the License, or
> +    (at your option) any later version.
> +
> +    This program is distributed in the hope that it will be useful,
> +    but WITHOUT ANY WARRANTY; without even the implied warranty of
> +    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.    See the
> +    GNU General Public License for more details.
> +
> +    You should have received a copy of the GNU General Public License
> +    along with this program; if not, write to the Free Software
> +    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
> +*/
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/slab.h>
> +#include <linux/jiffies.h>
> +#include <linux/i2c.h>
> +#include <linux/hwmon.h>
> +#include <linux/hwmon-sysfs.h>
> +#include <linux/err.h>
> +#include <linux/mutex.h>
> +
> +/* Addresses to scan */
> +static unsigned short normal_i2c[] = { 0x48, 0x49, 0x4a, 0x4b,
> +    I2C_CLIENT_END };
> +
> +/* Insmod parameters */
> +I2C_CLIENT_INSMOD_1(ads7828);
> +
> +/* The ADS7828 registers */
> +#define ADS7828_NCH 8 /* 8 channels of 12bit A-D supported */
> +#define ADS7828_CMD_SD_SE 0x80 /* Single ended inputs */
> +#define ADS7828_CMD_SD_DIFF 0x00 /* Differential inputs */
> +#define ADS7828_CMD_PD0 0x0 /* Power Down between A-D conversions */
> +#define ADS7828_CMD_PD1 0x04 /* Internal ref OFF && A-D ON */
> +#define ADS7828_CMD_PD2 0x08 /* Internal ref ON && A-D OFF */
> +#define ADS7828_CMD_PD3 0x0C /* Internal ref ON && A-D ON */
> +#define ADS7828_INT_VREF 2500 /* Internal vref is 2.5v, 2500mV */
> +
> +/* module parameters */
> +static int ads7828_se_input = 1; /* Default is SE, 0 == diff */
> +static int ads7828_int_vref = 1; /* Default is internal ref ON */
> +static int ads7828_vref = ADS7828_INT_VREF; /* set if vref != 2.5v */
> +module_param(ads7828_se_input, bool, S_IRUGO);
> +module_param(ads7828_int_vref, bool, S_IRUGO);
> +module_param(ads7828_vref, int, S_IRUGO);
> +
> +static u8 ads7828_cmd_byte; /* cmd byte without channel bits */
> +static unsigned int ads7828_lsb_resol; /* resolution of the ADC sample lsb */

What's the unit of ads7828_lsb_resol?

All these parameters deserve some documentation in
Documentation/hwmon/ads7828. See the other files in this directory for
the expected format. Note that it is usual to not include the driver
name in the parameter names.

> +
> +/* Each client has this additional data */
> +struct ads7828_data {
> +    struct i2c_client client;
> +    struct class_device *class_dev;
> +    struct mutex update_lock; /* mutex protect updates */
> +    char valid; /* !=0 if following fields are valid */
> +    unsigned long last_updated; /* In jiffies */
> +    u16 adc_input[ADS7828_NCH]; /* ADS7828_NCH 12bit samples */
> +};
> +
> +static int ads7828_attach_adapter(struct i2c_adapter *adapter);
> +static int ads7828_detect(struct i2c_adapter *adapter, int address, int 
> kind);
> +static void ads7828_init_client(struct i2c_client *client);
> +static int ads7828_detach_client(struct i2c_client *client);
> +static struct ads7828_data *ads7828_update_device(struct device *dev);
> +static u16 ads7828_read_value(struct i2c_client *client, u8 reg);
> +
> +/* This is the driver that will be inserted */
> +static struct i2c_driver ads7828_driver = {
> +    .driver = {
> +        .name = "ads7828",
> +    },
> +    .id = I2C_DRIVERID_ADS7828,

What do you need this ID for? The I2C driver ID is optional and in most
cases hardware monitoring-drivers don't need any, so you can just omit it.

> +    .attach_adapter = ads7828_attach_adapter,
> +    .detach_client = ads7828_detach_client,
> +};
> +
> +static ssize_t show_in(struct device *dev, struct device_attribute *da,
> +    char *buf)
> +{
> +    struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
> +    struct ads7828_data *data = ads7828_update_device(dev);
> +    /* Print value (in mv as specified in sysctl-interface documentation) */

sysfs, not sysctl.

> +    return sprintf(buf, "%d\n", (data->adc_input[attr->index] *
> +        ads7828_lsb_resol)/1000);
> +}
> +
> +#define in_reg(offset)\
> +static SENSOR_DEVICE_ATTR(in##offset##_input, S_IRUGO, show_in,\
> +    NULL, offset);
> +
> +in_reg(0);
> +in_reg(1);
> +in_reg(2);
> +in_reg(3);
> +in_reg(4);
> +in_reg(5);
> +in_reg(6);
> +in_reg(7);
> +
> +static int ads7828_attach_adapter(struct i2c_adapter *adapter)
> +{
> +    if (!(adapter->class & I2C_CLASS_HWMON))
> +        return 0;
> +    return i2c_probe(adapter, &addr_data, ads7828_detect);
> +}
> +
> +static struct attribute *ads7828_attributes[] = {
> +    &sensor_dev_attr_in0_input.dev_attr.attr,
> +    &sensor_dev_attr_in1_input.dev_attr.attr,
> +    &sensor_dev_attr_in2_input.dev_attr.attr,
> +    &sensor_dev_attr_in3_input.dev_attr.attr,
> +    &sensor_dev_attr_in4_input.dev_attr.attr,
> +    &sensor_dev_attr_in5_input.dev_attr.attr,
> +    &sensor_dev_attr_in6_input.dev_attr.attr,
> +    &sensor_dev_attr_in7_input.dev_attr.attr,
> +    NULL
> +};
> +
> +static const struct attribute_group ads7828_group = {
> +    .attrs = ads7828_attributes,
> +};
> +
> +/* This function is called by i2c_detect */
> +static int ads7828_detect(struct i2c_adapter *adapter, int address, int 
> kind)
> +{
> +    struct i2c_client *new_client;

Please rename this to just "client".

> +    struct ads7828_data *data;
> +    int err = 0, ch = 0;

ch doesn't need to be initialized here. (In fact it doesn't even need
to be declared here - same for cmd and in_data below.)

> +    const char *name = "";
> +    u8 cmd;
> +    u16 in_data;
> +
> +    /* Check we have a valid client */
> +    if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
> +                         I2C_FUNC_SMBUS_WORD_DATA))

You're not using byte-size transactions, and you're never writing to
the device, so I2C_FUNC_SMBUS_READ_WORD_DATA is enough.

> +        goto exit;
> +
> +    /* OK. For now, we presume we have a valid client. We now create the
> +         client structure, even though we cannot fill it completely yet.
> +         But it allows us to access ads7828_read_value. */
> +    data = kmalloc(sizeof(struct ads7828_data), GFP_KERNEL);
> +    if (!data)
> +        err = -ENOMEM;
> +        goto exit;
> +    }
> +    memset(data, 0, sizeof(struct ads7828_data));
> +
> +    new_client = &data->client;
> +    i2c_set_clientdata(new_client, data);
> +    new_client->addr = address;
> +    new_client->adapter = adapter;
> +    new_client->driver = &ads7828_driver;
> +    new_client->flags = 0;

This is redundant with the above memset (or kzalloc).

> +
> +    /* Perform local initialisation */
> +    ads7828_init_client(new_client);
> +
> +    /* Now, we do the remaining detection. There is no identification
> +    dedicated register so attempt to sanity check using knowledge of 
> the chip
> +    - Read from the 8 channel addresses
> +    - Check the top 4 bits of each result are not set (12 data bits)
> +    */
> +    if (kind < 0) {
> +        for (ch = 0; ch < ADS7828_NCH; ch++) {
> +            /* cmd byte C2,C1,C0 - see datasheet */
> +            cmd = (((ch>>1) | (ch&0x01)<<2)<<4);

You're using this formula several times in the driver, it would
probably be worth having a macro or even better, an inline function for
it.

> +            cmd |= ads7828_cmd_byte;
> +            in_data = ads7828_read_value(new_client, cmd);
> +            if (in_data & 0xF000) {
> +                printk(KERN_DEBUG
> +                "%s : Doesn't look like an ads7828 device\n",
> +                __FUNCTION__);

Please use dev_dbg(&adapter->dev, ...) instead, that way the user knows
what I2C bus was being probed. It might also be a good idea to include
the chip address in the log message. The function name OTOH doesn't
seem particularly useful to me.

> +                goto exit_free;
> +            }
> +        }
> +    }
> +
> +    /* Determine the chip type - only one kind supported! */
> +    if (kind <= 0)
> +        kind = ads7828;
> +
> +    if (kind == ads7828)
> +        name = "ads7828";
> +
> +    /* Fill in the remaining client fields, put it into the global list */
> +    strlcpy(new_client->name, name, I2C_NAME_SIZE);
> +    data->valid = 0;

Redundant.

> +    mutex_init(&data->update_lock);
> +
> +    /* Tell the I2C layer a new client has arrived */
> +    err = i2c_attach_client(new_client);
> +    if (err)
> +        goto exit_free;
> +
> +    /* Register sysfs hooks */
> +    err = sysfs_create_group(&new_client->dev.kobj, &ads7828_group);
> +    if (err)
> +        goto exit_detach;
> +
> +    data->class_dev = hwmon_device_register(&new_client->dev);
> +    if (IS_ERR(data->class_dev)) {
> +        err = PTR_ERR(data->class_dev);
> +        goto exit_remove;
> +    }
> +
> +    return 0;
> +
> +exit_remove:
> +    sysfs_remove_group(&new_client->dev.kobj, &ads7828_group);
> +exit_detach:
> +    i2c_detach_client(new_client);
> +exit_free:
> +    kfree(data);
> +exit:
> +    return err;
> +}
> +
> +static int ads7828_detach_client(struct i2c_client *client)
> +{
> +    struct ads7828_data *data = i2c_get_clientdata(client);
> +    hwmon_device_unregister(data->class_dev);
> +    sysfs_remove_group(&client->dev.kobj, &ads7828_group);
> +    i2c_detach_client(client);
> +    kfree(i2c_get_clientdata(client));
> +    return 0;
> +}
> +
> +/* The ADS7828 returns the 12bit sample in two bytes,
> +    these are read as a word then byte-swapped */
> +static u16 ads7828_read_value(struct i2c_client *client, u8 reg)
> +{
> +    u16 buffer = i2c_smbus_read_word_data(client, reg);
> +    return ((buffer&0xFF)<<8) | ((buffer&0xFF00)>>8);

Please use swab16(), as the lm75 driver and many others do.

> +}
> +
> +static void ads7828_init_client(struct i2c_client *client)
> +{
> +    /* Initialise the command byte according to module parameters */
> +    ads7828_cmd_byte = ads7828_se_input ?
> +        ADS7828_CMD_SD_SE : ADS7828_CMD_SD_DIFF;
> +    ads7828_cmd_byte |= ads7828_int_vref ?
> +        ADS7828_CMD_PD3 : ADS7828_CMD_PD1;
> +
> +    /* Calculate the LSB resolution */
> +    ads7828_lsb_resol = (ads7828_vref*1000)/4096;

It doesn't make sense to initialize these values as part of the device
initialization, given that these are global variables that are shared
by all devices. Either make these per-device values, or initialize them
on driver load (in sensors_ads7828_init.)

> +}
> +
> +static struct ads7828_data *ads7828_update_device(struct device *dev)
> +{
> +    struct i2c_client *client = to_i2c_client(dev);
> +    struct ads7828_data *data = i2c_get_clientdata(client);
> +    unsigned int cmd, ch;
> +
> +    mutex_lock(&data->update_lock); /* LOCK */
> +
> +    if (time_after(jiffies, data->last_updated + HZ + HZ / 2)
> +            || !data->valid) {
> +        dev_dbg(&client->dev, "Starting ads7828 update\n");
> +
> +        for (ch = 0; ch < ADS7828_NCH; ch++) {
> +            /* cmd byte C2,C1,C0 - see datasheet */
> +            cmd = (((ch>>1) | (ch&0x01)<<2)<<4);
> +            cmd |= ads7828_cmd_byte;
> +            data->adc_input[ch] = ads7828_read_value(client, cmd);
> +        }
> +        data->last_updated = jiffies;
> +        data->valid = 1;
> +    }
> +
> +    mutex_unlock(&data->update_lock); /* UNLOCK */
> +
> +    return data;
> +}
> +
> +static int __init sensors_ads7828_init(void)
> +{
> +    return i2c_add_driver(&ads7828_driver);
> +}
> +
> +static void __exit sensors_ads7828_exit(void)
> +{
> +    i2c_del_driver(&ads7828_driver);
> +}
> +
> +MODULE_AUTHOR("Steve Hardy <steve@...uxrealtime.co.uk");

Missing ">".

> +MODULE_DESCRIPTION("ADS7828 driver");
> +MODULE_LICENSE("GPL");
> +
> +module_init(sensors_ads7828_init);
> +module_exit(sensors_ads7828_exit);


-- 
Jean Delvare
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