2017-03-29 09:31:02

by Tobias Regnery

Subject: [PATCH] drm/i915: fix build error without CONFIG_BACKLIGHT_CLASS_DEVICE

With CONFIG_ACPI=n and CONFIG_BACKLIGHT_CLASS_DEVICE=n we see the following
link error in the i915 driver:

drivers/built-in.o: In function 'intel_backlight_device_register':
(.text+0x2a921d): undefined reference to 'backlight_device_register'

Fix this by removing the condition on ACPI from the appropriate select
statement.

Signed-off-by: Tobias Regnery <[email protected]>
---
drivers/gpu/drm/i915/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
index a5cd5dacf055..532df4bb9283 100644
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -15,7 +15,7 @@ config DRM_I915
# i915 depends on ACPI_VIDEO when ACPI is enabled
# but for select to work, need to select ACPI_VIDEO's dependencies, ick
select BACKLIGHT_LCD_SUPPORT if ACPI
- select BACKLIGHT_CLASS_DEVICE if ACPI
+ select BACKLIGHT_CLASS_DEVICE
select INPUT if ACPI
select ACPI_VIDEO if ACPI
select ACPI_BUTTON if ACPI
--
2.11.0

2017-03-30 06:52:26

by Jani Nikula

Subject: Re: [PATCH] drm/i915: fix build error without CONFIG_BACKLIGHT_CLASS_DEVICE

On Wed, 29 Mar 2017, Tobias Regnery <[email protected]> wrote:
> With CONFIG_ACPI=n and CONFIG_BACKLIGHT_CLASS_DEVICE=n we see the following
> link error in the i915 driver:
>
> drivers/built-in.o: In function 'intel_backlight_device_register':
> (.text+0x2a921d): undefined reference to 'backlight_device_register'
>
> Fix this by removing the condition on ACPI from the appropriate select
> statement.

The right fix for the build problem is to add empty stub functions for
BACKLIGHT_CLASS_DEVICE=n in include/linux/backlight.h. I'm frankly
surprised nobody's done that yet.

It's another question whether we should support and select backlight for
ACPI=n, and yet another question whether we should support ACPI=n.

Also, selecting BACKLIGHT_CLASS_DEVICE is fundamentally broken, but
people aren't interested [1].


BR,
Jani.

[1] http://mid.mail-archive.com/[email protected]

>
> Signed-off-by: Tobias Regnery <[email protected]>
> ---
> drivers/gpu/drm/i915/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> index a5cd5dacf055..532df4bb9283 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -15,7 +15,7 @@ config DRM_I915
> # i915 depends on ACPI_VIDEO when ACPI is enabled
> # but for select to work, need to select ACPI_VIDEO's dependencies, ick
> select BACKLIGHT_LCD_SUPPORT if ACPI
> - select BACKLIGHT_CLASS_DEVICE if ACPI
> + select BACKLIGHT_CLASS_DEVICE
> select INPUT if ACPI
> select ACPI_VIDEO if ACPI
> select ACPI_BUTTON if ACPI

--
Jani Nikula, Intel Open Source Technology Center

2017-03-31 06:38:31

by Tobias Regnery

Subject: Re: [PATCH] drm/i915: fix build error without CONFIG_BACKLIGHT_CLASS_DEVICE

On 30.03.17, Jani Nikula wrote:
> On Wed, 29 Mar 2017, Tobias Regnery <[email protected]> wrote:
> > With CONFIG_ACPI=n and CONFIG_BACKLIGHT_CLASS_DEVICE=n we see the following
> > link error in the i915 driver:
> >
> > drivers/built-in.o: In function 'intel_backlight_device_register':
> > (.text+0x2a921d): undefined reference to 'backlight_device_register'
> >
> > Fix this by removing the condition on ACPI from the appropriate select
> > statement.
>
> The right fix for the build problem is to add empty stub functions for
> BACKLIGHT_CLASS_DEVICE=n in include/linux/backlight.h. I'm frankly
> surprised nobody's done that yet.

Thanks for the advice, I will try to come up with a patch.

--
Tobias

>
> It's another question whether we should support and select backlight for
> ACPI=n, and yet another question whether we should support ACPI=n.
>
> Also, selecting BACKLIGHT_CLASS_DEVICE is fundamentally broken, but
> people aren't interested [1].
>
>
> BR,
> Jani.
>
> [1] http://mid.mail-archive.com/[email protected]
>
> >
> > Signed-off-by: Tobias Regnery <[email protected]>
> > ---
> > drivers/gpu/drm/i915/Kconfig | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> > index a5cd5dacf055..532df4bb9283 100644
> > --- a/drivers/gpu/drm/i915/Kconfig
> > +++ b/drivers/gpu/drm/i915/Kconfig
> > @@ -15,7 +15,7 @@ config DRM_I915
> > # i915 depends on ACPI_VIDEO when ACPI is enabled
> > # but for select to work, need to select ACPI_VIDEO's dependencies, ick
> > select BACKLIGHT_LCD_SUPPORT if ACPI
> > - select BACKLIGHT_CLASS_DEVICE if ACPI
> > + select BACKLIGHT_CLASS_DEVICE
> > select INPUT if ACPI
> > select ACPI_VIDEO if ACPI
> > select ACPI_BUTTON if ACPI
>
> --
> Jani Nikula, Intel Open Source Technology Center