On Tue, 04 Oct 2022, "Jiri Slaby (SUSE)" <jirislaby@xxxxxxxxxx> wrote:
> When DRM_I915=y and BACKLIGHT_CLASS_DEVICE=m, the build fails:
> ld: drivers/gpu/drm/i915/display/intel_backlight.o: in function `intel_backlight_device_register':
> intel_backlight.c:(.text+0x5587): undefined reference to `backlight_device_get_by_name'
>
> ld: drivers/gpu/drm/i915/display/intel_backlight.o: in function `intel_backlight_device_unregister':
> intel_backlight.c:(.text+0x576e): undefined reference to `backlight_device_unregister'
>
> To fix this, use IS_REACHABLE(), not IS_ENABLED() in backlight. That is,
> with the above config, backlight support is disabled.
So I don't want this. I'll take a patch that fixes the dependencies to
block DRM_I915=y and BACKLIGHT_CLASS_DEVICE=m. Nobody wants that combo,
and IMO using IS_REACHABLE() is a workaround to hide a broken config
under the carpet.
The right thing to do is
config DRM_I915
depends on BACKLIGHT_CLASS_DEVICE || BACKLIGHT_CLASS_DEVICE=n.
We're selecting BACKLIGHT_CLASS_DEVICE because almost everyone else is
too, and a combo of selecting and depending leads to circular
dependencies. But depending is the right fix.
Documentation/kbuild/kconfig-language.rst:
Note:
select should be used with care. select will force
a symbol to a value without visiting the dependencies.
By abusing select you are able to select a symbol FOO even
if FOO depends on BAR that is not set.
In general use select only for non-visible symbols
(no prompts anywhere) and for symbols with no dependencies.
That will limit the usefulness but on the other hand avoid
the illegal configurations all over.
BR,
Jani.
>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Reported-by: Martin Liška <mliska@xxxxxxx>
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@xxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_backlight.c | 2 +-
> drivers/gpu/drm/i915/display/intel_backlight.h | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
> index beba39a38c87..c1ba68796b6d 100644
> --- a/drivers/gpu/drm/i915/display/intel_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_backlight.c
> @@ -825,7 +825,7 @@ void intel_backlight_enable(const struct intel_crtc_state *crtc_state,
> mutex_unlock(&dev_priv->display.backlight.lock);
> }
>
> -#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
> +#if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
> static u32 intel_panel_get_backlight(struct intel_connector *connector)
> {
> struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> diff --git a/drivers/gpu/drm/i915/display/intel_backlight.h b/drivers/gpu/drm/i915/display/intel_backlight.h
> index 339643f63897..207fe1c613d8 100644
> --- a/drivers/gpu/drm/i915/display/intel_backlight.h
> +++ b/drivers/gpu/drm/i915/display/intel_backlight.h
> @@ -36,7 +36,7 @@ u32 intel_backlight_invert_pwm_level(struct intel_connector *connector, u32 leve
> u32 intel_backlight_level_to_pwm(struct intel_connector *connector, u32 level);
> u32 intel_backlight_level_from_pwm(struct intel_connector *connector, u32 val);
>
> -#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
> +#if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
> int intel_backlight_device_register(struct intel_connector *connector);
> void intel_backlight_device_unregister(struct intel_connector *connector);
> #else /* CONFIG_BACKLIGHT_CLASS_DEVICE */
--
Jani Nikula, Intel Open Source Graphics Center
