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

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Date:	Wed, 2 Dec 2015 09:20:58 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Marc Titinger <mtitinger@...libre.com>
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 12/02/2015 09:09 AM, Marc Titinger wrote:
> 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
>
Can't do that.

> Anyone knows how to implement a radio button in Kconfig ? ;)
>
That is possible, but only in a single menu. Look for choice/endchoice.

Guenter

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