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

[Daniel Vetter]

On Sat, Sep 30, 2017 at 03:49:43PM +0200, Noralf Trønnes wrote:
> 
> 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.

Adding Jani to double-check this plan ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch