Re: [PATCH 1/2] drm/i915/display: fix randconfig build

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On 04. 10. 22, 12:52, Jani Nikula wrote:
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.

I'm not sure what should I do now. If I do:
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -4,6 +4,7 @@ config DRM_I915
        depends on DRM
        depends on X86 && PCI
        depends on !PREEMPT_RT
+ depends on (BACKLIGHT_CLASS_DEVICE && ACPI) || (BACKLIGHT_CLASS_DEVICE=n && ACPI=n)
        select INTEL_GTT if X86
        select INTERVAL_TREE
        # we need shmfs for the swappable backing store, and in particular
@@ -21,7 +22,6 @@ config DRM_I915
        select IRQ_WORK
        # i915 depends on ACPI_VIDEO when ACPI is enabled
# but for select to work, need to select ACPI_VIDEO's dependencies, ick
-       select BACKLIGHT_CLASS_DEVICE if ACPI
        select INPUT if ACPI
        select X86_PLATFORM_DEVICES if ACPI
        select ACPI_WMI if ACPI

I get:
drivers/gpu/drm/i915/Kconfig:2:error: recursive dependency detected!
drivers/gpu/drm/i915/Kconfig:2: symbol DRM_I915 depends on BACKLIGHT_CLASS_DEVICE drivers/video/backlight/Kconfig:143: symbol BACKLIGHT_CLASS_DEVICE is selected by DRM_FSL_DCU drivers/gpu/drm/fsl-dcu/Kconfig:2: symbol DRM_FSL_DCU depends on COMMON_CLK
drivers/clk/Kconfig:21: symbol COMMON_CLK is selected by X86_INTEL_QUARK
arch/x86/Kconfig:633: symbol X86_INTEL_QUARK depends on X86_PLATFORM_DEVICES drivers/platform/x86/Kconfig:6: symbol X86_PLATFORM_DEVICES is selected by DRM_I915


Those dependencies are really cumbersome :/.

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 */


--
js
suse labs




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