linux-kernel - Re: [PATCH v2 1/2] iio: ina2xx: add support for TI INA2xx Power Monitors

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Message-ID: <565F25D4.10006@baylibre.com>
Date:	Wed, 2 Dec 2015 18:09:40 +0100
From:	Marc Titinger <mtitinger@...libre.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	pmeerw@...erw.net, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iio: ina2xx: add support for TI INA2xx Power
 Monitors

On 02/12/2015 17:44, Guenter Roeck wrote:
> On 12/02/2015 08:20 AM, Marc Titinger wrote:
>> On 02/12/2015 17:04, Guenter Roeck wrote:
>>> On 12/02/2015 02:20 AM, Marc Titinger wrote:
>>>> On 02/12/2015 03:14, Guenter Roeck wrote:
>>>>> On Mon, Nov 30, 2015 at 12:49:14PM +0100, Marc Titinger wrote:
>>>>>> in SOFTWARE buffer mode, a kthread will capture the active
>>>>>> scan_elements
>>>>>> into a kfifo, then compute the remaining time until the next capture
>>>>>> tick
>>>>>> and do an active wait (udelay).
>>>>>>
>>>>>> This will produce a stream of up to fours channels plus a 64bits
>>>>>> timestamps (ns).
>>>>>>
>>>>>> Tested with ina226, on BeagleBoneBlack.
>>>>>>
>>>>>> Datasheet: http://www.ti.com/lit/gpn/ina226
>>>>>>
>>>>>> Signed-off-by: Marc Titinger <mtitinger@...libre.com>
>>>>>> ---
>>>>>>   drivers/iio/adc/Kconfig      |   9 +
>>>>>>   drivers/iio/adc/Makefile     |   1 +
>>>>>>   drivers/iio/adc/ina2xx-iio.c | 678
>>>>>> +++++++++++++++++++++++++++++++++++++++++++
>>>>>>   3 files changed, 688 insertions(+)
>>>>>>   create mode 100644 drivers/iio/adc/ina2xx-iio.c
>>>>>> +
>>>>> [ ... ]
>>>>>> +
>>>>>> +static const struct i2c_device_id ina2xx_id[] = {
>>>>>> +    {"ina219", ina219},
>>>>>> +    {"ina220", ina219},
>>>>>> +    {"ina226", ina226},
>>>>>> +    {"ina230", ina226},
>>>>>> +    {"ina231", ina226},
>>>>>> +    {}
>>>>>> +};
>>>>>
>>>>> I wonder what is going to happen if both this driver and the hwmon
>>>>> driver for the same chips are configured in a system which supports
>>>>> devicetree (or any system, really). Unless I am missing something,
>>>>> the result will be that both drivers will try to instantiate, and
>>>>> one will fail with -EBUSY. Or the instantiated driver is more or less
>>>>> random, depending on which one happens to be loaded. Not a good
>>>>> situation to be in.
>>>>
>>>> I agree, we should put a mutual exclusion in Kconfig, plus maybe a
>>>> cross-reference in the help section.
>>>>
>>>>>
>>>>> For the time being, it might make sense to add cross-dependencies
>>>>> in Kconfig to only permit one of the two drivers to be configured.
>>>>>
>>>>> Ultimately we may need a better solution for the iio-hwmon bridge,
>>>>> one that makes the underlying driver transparent in both devicetree
>>>>> properties and user space ABI. No idea how to do that, though.
>>>>>
>>>>
>>>> IDK if ina2xx is a special case or if this matter of dual driver
>>>> stacks for the same chip already occurred and requires specific
>>>> plumbing. Making the user aware of the mutual of the exclusion sounds
>>>> fine with me.
>>>>
>>> htu21. We'll drop that driver from hwmon with the 4.5 kernel.
>>> We could just drop ina2xx as well, but it is more widely used
>>> and referenced from dts files. The ABI changes, so I am not sure
>>> if we can just do that.
>>
>> I changed iio/adc/Kconfig to the following:
>>
>> +config INA2XX_ADC
>> +       tristate "Texas Instruments INA2xx Power Monitors IIO driver"
>> +       depends on I2C && !SENSORS_INA2XX
>> +       select REGMAP_I2C
>> +       select IIO_BUFFER
>> +       select IIO_KFIFO_BUF
>> +       help
>> +         Say yes here to build support for TI INA2xx family of Power
>> Monitors.
>> +         This driver is mutually exclusive with the HWMON version.
>> +
>>
>>
>> anything the patch should also add to hwmon/Kconfig (that will not
>> lead to a cycling reference warning) ?
>>
>
> You could try the opposite, but I don't know if that works.
>
>      depends on I2C && !INA2XX_ADC

I tried: it's functional, but leads to a ugly warning:

drivers/iio/adc/Kconfig:173:error: recursive dependency detected!
drivers/iio/adc/Kconfig:173:	symbol INA2XX_ADC depends on SENSORS_INA2XX
drivers/hwmon/Kconfig:1453:	symbol SENSORS_INA2XX depends on INA2XX_ADC

Anyone knows how to implement a radio button in Kconfig ? ;)


>
> Guenter
>

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