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Message-ID: <4EA53973.9080102@cam.ac.uk>
Date: Mon, 24 Oct 2011 11:09:55 +0100
From: Jonathan Cameron <jic23@....ac.uk>
To: Jonathan Cameron <jic23@....ac.uk>
CC: guenter.roeck@...csson.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
"linus.ml.walleij@...il.com" <linus.ml.walleij@...il.com>,
"zdevai@...il.com" <zdevai@...il.com>,
"linux@....linux.org.uk" <linux@....linux.org.uk>,
"arnd@...db.de" <arnd@...db.de>,
"broonie@...nsource.wolfsonmicro.com"
<broonie@...nsource.wolfsonmicro.com>,
"gregkh@...e.de" <gregkh@...e.de>,
"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
"khali@...ux-fr.org" <khali@...ux-fr.org>,
"thomas.petazzoni@...e-electrons.com"
<thomas.petazzoni@...e-electrons.com>,
"maxime.ripard@...e-electrons.com" <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH 5/6] IIO:hwmon interface client driver.
On 10/20/11 16:30, Jonathan Cameron wrote:
> On 10/20/11 16:12, Guenter Roeck wrote:
>> On Thu, 2011-10-20 at 05:33 -0400, Jonathan Cameron wrote:
>>> Should move to drivers/hwmon once people are happy with it.
>>>
>>> Minimal support of simple in, curr and temp attributes
>>> so far.
>>>
>>> Signed-off-by: Jonathan Cameron <jic23@....ac.uk>
>>> ---
>>> drivers/iio/Kconfig | 8 ++
>>> drivers/iio/Makefile | 1 +
>>> drivers/iio/iio_hwmon.c | 227 +++++++++++++++++++++++++++++++++++++++++++++++
>>> 3 files changed, 236 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
>>> index 308bc97..c2f0970 100644
>>> --- a/drivers/iio/Kconfig
>>> +++ b/drivers/iio/Kconfig
>>> @@ -11,6 +11,14 @@ menuconfig IIO
>>>
>>> if IIO
>>>
>>> +config IIO_HWMON
>>> + tristate "Hwmon driver that uses channels specified via iio maps"
>>> + depends on HWMON
>>> + help
>>> + This is a platform driver that in combination with a suitable
>>> + map allows IIO devices to provide basic hwmon functionality
>>> + for those channels specified in the map.
>>> +
>>> source "drivers/iio/adc/Kconfig"
>>> source "drivers/iio/imu/Kconfig"
>>> source "drivers/iio/light/Kconfig"
>>> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
>>> index cfb588a..5f9c01a 100644
>>> --- a/drivers/iio/Makefile
>>> +++ b/drivers/iio/Makefile
>>> @@ -6,6 +6,7 @@ obj-y = inkern.o
>>> obj-$(CONFIG_IIO) += iio.o
>>> industrialio-y := core.o
>>>
>>> +obj-$(CONFIG_IIO_HWMON) += iio_hwmon.o
>>> obj-y += adc/
>>> obj-y += imu/
>>> obj-y += light/
>>> diff --git a/drivers/iio/iio_hwmon.c b/drivers/iio/iio_hwmon.c
>>> new file mode 100644
>>> index 0000000..b3348ad
>>> --- /dev/null
>>> +++ b/drivers/iio/iio_hwmon.c
>>> @@ -0,0 +1,227 @@
>>> +/* Hwmon client for industrial I/O devices
>>> + *
>>> + * Copyright (c) 2011 Jonathan Cameron
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify it
>>> + * under the terms of the GNU General Public License version 2 as published by
>>> + * the Free Software Foundation.
>>> + *
>>> + * Limited functionality currently supported.
>>
>> Just nitpicking ... this comment doesn't provide much value. It doesn't
>> explain the limits, nor what could be improved.
>>
>>> + */
>>> +
>>> +#include <linux/kernel.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/module.h>
>>> +#include <linux/err.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/iio/inkern.h>
>>> +#include <linux/hwmon.h>
>>> +#include <linux/hwmon-sysfs.h>
>>> +
>>> +/**
>>> + * struct iio_hwmon_state - device instance state
>>> + * @channels: filled with null terminated array of channels from iio
>>> + * @num_channels: number of channels in channels (saves counting twice)
>>> + * @hwmon_dev: associated hwmon device
>>> + * @attr_group: the group of attributes
>>> + * @attrs: null terminated array of attribute pointers.
>>> + */
>>> +struct iio_hwmon_state {
>>> + struct iio_channel **channels;
>>> + int num_channels;
>>> + struct device *hwmon_dev;
>>> + struct attribute_group attr_group;
>>> + struct attribute **attrs;
>>> +};
>>> +
>>> +/*
>>> + * Assumes that IIO and hwmon operate in the same base units.
>>> + * This is supposed to be true, but needs verification for
>>> + * new channel types.
>>> + */
>>> +static ssize_t iio_hwmon_read_val(struct device *dev,
>>> + struct device_attribute *attr,
>>> + char *buf)
>>> +{
>>> + long result;
>>> + int val, ret, scaleint, scalepart;
>>> + struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);
>>> + struct iio_hwmon_state *state = dev_get_drvdata(dev);
>>> +
>>> + /*
>>> + * No locking between this pair, so theoretically possible
>>> + * the scale has changed.
>>> + */
>>> + ret = iio_read_channel_raw(state->channels[sattr->index],
>>> + &val);
>>> + if (ret < 0)
>>> + return ret;
>>> +
>>> + ret = iio_read_channel_scale(state->channels[sattr->index],
>>> + &scaleint, &scalepart);
>>> + if (ret < 0)
>>> + return ret;
>>> + switch (ret) {
>>> + case IIO_VAL_INT:
>>> + result = val * scaleint;
>>> + break;
>>> + case IIO_VAL_INT_PLUS_MICRO:
>>> + result = (long)val * (long)scaleint +
>>> + (long)val * (long)scalepart / 1000000L;
>>> + break;
>>> + case IIO_VAL_INT_PLUS_NANO:
>>> + result = (long)val * (long)scaleint +
>>> + (long)val * (long)scalepart / 1000000000L;
>>> + break;
>>
>> Still easy to imagine that val * scalepart gets larger than 2147483647L
>> (on machines where sizeof(long) = 4) ... it will already happen if the
>> result of (val * scalepart / 1000000000) is larger than 2.
> Good point. I really ought to have done the calcs.
> If we have maximum possible value in here things will be ugly.
>
> Worst case is scalepart is 9999999999. (could be done as 1 - 0.000000001
> which would be nicer, but we don't specify a preference - from this
> discussion I am suspecting we should!)
>
> Looks like 64 bits is going to be a requirement as you say.
>>
>> What value range do you expect to see here ?
>>
>> If (val * scaleint) is already the milli-unit, scalepart would possibly
>> only address fractions of milli-units. If so, the result of (val *
>> scalepart / 1000000000L) might always be smaller than 1, ie 0.
> It certainly should be.
>> If so, for the calculation to have any value, you might be better off using
>> DIV_ROUND_CLOSEST(val * scalepart, 1000000000L).
> Good idea.
>>
>> I am a bit confused by this anyway. Since hwmon in general reports
>> milli-units, VAL_INT appears to reflect milli-units, VAL_INT_PLUS_MICRO
>> really means nano-units, and IIO_VAL_INT_PLUS_NANO really means
>> pico-units. Is this correct ?
> Micro units of the scale factor.
>
> Take my test part a max1363...
> Scale is actually 0.5 so each adc count (e.g. raw value) is 0.5millivolts.
>
> scale int here is 0,
> scale part is 500,000 (so 0.5) and it returns IIO_VAL_INT_PLUS_MICRO.
How about the following? It'll be extremely costly, but this isn't exactly
a fast path!
case IIO_VAL_INT_PLUS_MICRO:
result = (s64)val * (s64)scaleint +
div_s64((s64)val * (s64)scalepart, 1000000LL);
break;
case IIO_VAL_INT_PLUS_NANO:
result = (s64)val * (s64)scaleint +
div_s64((s64)val * (s64)scalepart, 1000000000LL);
break;
Everything should fit in there and it should give us pretty good precision.
>
>
>>
>>> + default:
>>> + return -EINVAL;
>>> + }
>>> + return sprintf(buf, "%ld\n", result);
>>> +}
>>> +
>>> +static void iio_hwmon_free_attrs(struct iio_hwmon_state *st)
>>> +{
>>> + int i;
>>> + struct sensor_device_attribute *a;
>>> + for (i = 0; i < st->num_channels; i++)
>>> + if (st->attrs[i]) {
>>> + a = to_sensor_dev_attr(
>>> + container_of(st->attrs[i],
>>> + struct device_attribute,
>>> + attr));
>>> + kfree(a);
>>> + }
>>> +}
>>> +
>>> +static int __devinit iio_hwmon_probe(struct platform_device *pdev)
>>> +{
>>> + struct iio_hwmon_state *st;
>>> + struct sensor_device_attribute *a;
>>> + int ret, i;
>>> + int in_i = 1, temp_i = 1, curr_i = 1;
>>> +
>>> + st = kzalloc(sizeof(*st), GFP_KERNEL);
>>> + if (st == NULL) {
>>> + ret = -ENOMEM;
>>> + goto error_ret;
>>> + }
>>> +
>>> + st->channels = iio_channel_get_all(&pdev->dev, NULL);
>>> + if (IS_ERR(st->channels)) {
>>> + ret = PTR_ERR(st->channels);
>>> + goto error_free_state;
>>> + }
>>> +
>>> + /* count how many attributes we have */
>>> + while (st->channels[st->num_channels])
>>> + st->num_channels++;
>>> +
>>> + st->attrs = kzalloc(sizeof(st->attrs) * (st->num_channels + 1),
>>> + GFP_KERNEL);
>>
>> Why "+ 1" ?
> Null terminated list for attribute groups. Hence the kzalloc.
>>
>> Unless I am missing something, you only use st->attrs[0] ..
>> st->attrs[st->num_channels-1].
>>
>> Thanks,
>> Guenter
>>
>>
>>
>
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