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

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Message-ID: <20151202021429.GA19098@roeck-us.net>
Date:	Tue, 1 Dec 2015 18:14:29 -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 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.

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.

Guenter
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