Re: [PATCH 3/3] power: bq27xxx_battery: fix defined but not used warnings

[Sebastian Reichel <sre@kernel.org>]

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On Fri, Oct 16, 2015 at 10:01:33AM -0500, Andrew F. Davis wrote:
> On 10/16/2015 09:47 AM, Pali Rohár wrote:
> >On Friday 16 October 2015 15:44:12 Sebastian Reichel wrote:
> >>If BQ27XXX is enabled, but neither I2C based initialization, nor
> >>platform based initialization are activated, bq27xxx_powersupply_init
> >>and bq27xxx_powersupply_unregister are defined but not used.
> >>
> >>This configuration doesn't make sense, but there is no easy way
> >>to make it unavailable in the build system, so just mark the
> >>functions as __maybe_unused instead.
> >>
> >
> >What about?
> >
> >#if defined(CONFIG_1) || defined(CONFIG_2)
> >#define NEED_POWER_SUPPLY
> >#endif
> >
> >And then wrap power supply code into #ifdef NEED_POWER_SUPPLY?

I thought about wrapping the whole code in an ifdef, but I don't
think compiling an empty file is any better than adding the
__maybe_unused flag.

> We would need to wrap everything in that then, so without I2C or
> platform enabled we end up compiling an empty file. I think the
> better fix would be to modify the Kconfig, something like:

Handling this in Kconfig is preferred of course.

> config BATTERY_BQ27XXX
> 	tristate
> 	depends on (BATTERY_BQ27XXX_I2C || BATTERY_BQ27XXX_PLATFORM)
> 	default y
> 
> config BATTERY_BQ27XXX_I2C
> 	bool "BQ27200/BQ27500 support"
> 	depends on I2C
> 	help
> 	  Say Y here to enable support for batteries with BQ27x00 (I2C) chips.
> 
> config BATTERY_BQ27XXX_PLATFORM
> 	bool "BQ27000 support"
> 	help
> 	  Say Y here to enable support for batteries with BQ27000 (HDQ) chips.
> 
> This would be more in line with how other multi-bus devices handle
> this issue when nether bus is selected.

If I'm not mistaken, this way it's impossible to build the code as
module. You need to move the tristate to the individual bus options.
This would require to split the code, so that two separate modules
are built. I checked the tree and found a few examples:

 * building one modules for each bus, core support is autoselected, but always built-in
  - BMP085

 * building a core modules + one module for each bus
  - AD525X_DPOT
  - ADE7854
  - ADT7316
  - INPUT_AD714X
  - INPUT_ADXL34X
  - TOUCHSCREEN_AD7879
  - TOUCHSCREEN_CYTTSP_CORE
  - TOUCHSCREEN_CYTTSP4_CORE

Instead of restructuring the whole driver, we could also just built
the platform code unconditionally. The platform specific code is
just a probe + remove function and bq27xxx_battery_platform_read().
The last one could be dropped, if the pdata->read function is
modified (effectively moving the code into the w1 driver).

-- Sebastian

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