[PATCH v5 4/4] drm/tinydrm: select BACKLIGHT_LCD_SUPPORT, BACKLIGHT_CLASS_DEVICE

[Noralf Trønnes]

Den 30.09.2017 11.10, skrev Meghana Madhyastha:
> Add select BACKLIGHT_LCD_SUPPORT, BACKLIGHT_CLASS_DEVICE to
> the Kconfig of drm. This is required for the successful build of
> drm_of_find_backlight helpers.
>
> Signed-off-by: Meghana Madhyastha <meghana.madhyastha at gmail.com>
> ---
> Changes in v5:
> -This commit was not present in v4. Selecting BACKLIGHT_LCD_SUPPORT,
> BACKLIGHT_CLASS_DEVICE in the Kconfig file under the symbol DRM seems
> to fix the Kbuild error drm_of.c:(.text+0x3bc): undefined reference to
> `of_find_backlight_by_node'.
>
>   drivers/gpu/drm/Kconfig | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 83cb2a8..3ba5632 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -7,6 +7,8 @@
>   menuconfig DRM
>   	tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
>   	depends on (AGP || AGP=n) && !EMULATED_CMPXCHG && HAS_DMA
> +	select BACKLIGHT_LCD_SUPPORT
> +	select BACKLIGHT_CLASS_DEVICE
>   	select HDMI
>   	select FB_CMDLINE
>   	select I2C

A night's sleep has made this more clear, we don't need 'depends on'
or select as you have tried here, it's enough that we make a change in
the backlight subsystem as I outlined earlier:

include/linux/backlight.h:

-#ifdef CONFIG_OF
+#if defined(CONFIG_OF) && IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
  struct backlight_device *of_find_backlight_by_node(struct device_node 
*node);
  #else
  static inline struct backlight_device *
  of_find_backlight_by_node(struct device_node *node)
  {
      return NULL;
  }
  #endif

Now we don't have to care about backlight being built-in, module or 
disabled.

This patch has to be the first in the patchset. No single patch can 
break anything
even if it's fixed later. This is so people can bisect.

Noralf.