Date:	Wed, 2 Dec 2015 08:44:40 -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 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

Guenter

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