linux-kernel - Re: [PATCH/RFC v4 15/21] media: Add registration helpers for V4L2 flash

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Date:	Thu, 21 Aug 2014 10:38:34 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Sakari Ailus <sakari.ailus@....fi>
Cc:	linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	kyungmin.park@...sung.com, b.zolnierkie@...sung.com,
	Hans Verkuil <hans.verkuil@...co.com>
Subject: Re: [PATCH/RFC v4 15/21] media: Add registration helpers for V4L2 flash

Hi Sakari,

On 08/20/2014 04:41 PM, Sakari Ailus wrote:
> Hi Jacek,

[...]
>>>>
>>>> LED Class Flash driver gains V4L2 Flash API when
>>>> CONFIG_V4L2_FLASH_LED_CLASS is defined. This is accomplished in
>>>> the probe function by either calling v4l2_flash_init function
>>>> or the macro of this name, when the CONFIG_V4L2_FLASH_LED_CLASS
>>>> macro isn't defined.
>>>>
>>>> If the v4l2-flash.c was to call the LED API directly, then the
>>>> led-class-flash module symbols would have to be available at
>>>> v4l2-flash.o linking time.
>>>
>>> Is this an issue? EXPORT_SYMBOL_GPL() for the relevant symbols should be
>>> enough.
>>
>> It isn't enough. If I call e.g. led_set_flash_brightness
>> directly from v4l2-flash.c and configure led-class-flash to be built as
>> a module then I am getting "undefined reference to
>> led_set_flash_brightness" error during linking phase.
>
> You should not. You also should change the check as (unless you've changed
> it already):
>
> #if IS_ENABLED(CONFIG_V4L2_FLASH_LED_CLASS)
>
> This will evaluate to non-zero if the macro arguent or the argument
> postfixed with "_MODULE" is defined.

I've missed this macro. Indeed, it is possible to avoid the need
for ops with it. I will fix it in the next version of the patch set.
Thanks for the hint.

Best Regards,
Jacek Anaszewski

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