[PATCH] backlight: add PWM dependencies

Linus Walleij linus.walleij at linaro.org
Wed Feb 5 03:57:32 EST 2014

On Wed, Feb 5, 2014 at 6:01 AM, Jingoo Han <jg1.han at samsung.com> wrote:
> On Tuesday, February 04, 2014 9:57 PM, Linus Walleij wrote:
>> In some compilations the LM3630A and LP855X backlight drivers
>> fail like this:
>> drivers/built-in.o: In function `lm3630a_pwm_ctrl':
>> drivers/video/backlight/lm3630a_bl.c:168: undefined reference to `pwm_config'
>> drivers/video/backlight/lm3630a_bl.c:172: undefined reference to `pwm_disable'
>> drivers/video/backlight/lm3630a_bl.c:170: undefined reference to `pwm_enable'
>> drivers/built-in.o: In function `lp855x_pwm_ctrl':
>> drivers/video/backlight/lp855x_bl.c:249: undefined reference to `pwm_config'
>> drivers/video/backlight/lp855x_bl.c:253: undefined reference to `pwm_disable'
>> drivers/video/backlight/lp855x_bl.c:251: undefined reference to `pwm_enable'
>> This is because both drivers depend on the PWM framework, so
>> add this dependency to their Kconfig entries.
> However, even though, when CONFIG_PWM is not enabled, the problem
> should not happen. pwm_config(),pwm_disable(), and pwm_enable()
> are already defined for CONFIG_PWM=n case as below.

So you may think but it does happen :-)

I reproduced this with the defconfig for ARM pxa255-idp and enabling
all boards for that platform, then enabling all available backlight drivers
as compiled-in objects (y).

> ./include/linux/pwm.h
>         .....
> #else

Hm PXA that I am using defines CONFIG_HAVE_PWM, but doesn't
provide the required signatures (pwm_config/pwm_disable/pwm_enable).

One of two things is wrong:

- Either the PXA platform is breaking the CONFIG_HAVE_PWM
  contract by not providing pwm_config/pwm_disable/pwm_enable
  functions. Then HAVE_PWM should be removed from the PXA
  Kconfig selects.


- There is no such contract that these functions must exist if
  CONFIG_HAVE_PWM is defined, and the
  should be removed from <linux/pwm.h>

Does anyone know which one it is?

PWM subsystem maintainer? :-)

Linus Walleij

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