On Wed, 08 Jan 2020, Arnd Bergmann arnd@arndb.de wrote:
The i915 driver can use the backlight subsystem as an option, and usually selects it when CONFIG_ACPI is set. However it is possible to configure a kernel with modular backlight classdev support and a built-in i915 driver, which leads to a linker error:
drivers/gpu/drm/i915/display/intel_panel.o: In function `intel_backlight_device_register': intel_panel.c:(.text+0x2f58): undefined reference to `backlight_device_register' drivers/gpu/drm/i915/display/intel_panel.o: In function `intel_backlight_device_unregister': intel_panel.c:(.text+0x2fe4): undefined reference to `backlight_device_unregister'
Add another Kconfig option to ensure the driver only tries to use the backlight support when it can in fact be linked that way. The new option is on by default to keep the existing behavior.
This is roughly what other drivers like nouveau do as well.
Signed-off-by: Arnd Bergmann arnd@arndb.de
I've had this one lying around for a long time, it is still needed but I am not sure which solution is best here. This version is probably the least invasive, but it does not solve the bigger problem around too many 'select' statements in drm
This is just another hack that's only required because backlight is selected instead of depended on throughout the kernel. (*)
i915 (and most drm drivers, with some variations) could easily handle this with:
depends on (ACPI && ACPI_VIDEO) || ACPI=n depends on BACKLIGHT_CLASS_DEVICE || BACKLIGHT_CLASS_DEVICE=n
Those two lines express the allowed configurations. It's just that we can't do that in i915 *alone*. The combinations of depends and selects lead to impossible configurations. It's all or nothing.
I am not amused by adding more hacks, and I am really *not* interested in adding another useless i915 config option to "solve" this issue.
So thanks, but no thanks. I'm not taking this patch.
BR, Jani.
(*) The deeper issue is that people as well as the kconfig tools ignore the warnings in Documentation/kbuild/kconfig-language.rst:
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.
I don't think we can, uh, fix the people, but it might be possible to warn about selecting visible symbols or symbols with dependencies.
drivers/gpu/drm/i915/Kconfig | 11 ++++++++++- drivers/gpu/drm/i915/display/intel_panel.c | 4 ++-- drivers/gpu/drm/i915/display/intel_panel.h | 6 +++--- 3 files changed, 15 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig index ba9595960bbe..81d956040d18 100644 --- a/drivers/gpu/drm/i915/Kconfig +++ b/drivers/gpu/drm/i915/Kconfig @@ -16,7 +16,7 @@ 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 DRM_I915_BACKLIGHT if ACPI select INPUT if ACPI select ACPI_VIDEO if ACPI select ACPI_BUTTON if ACPI
@@ -68,6 +68,15 @@ config DRM_I915_FORCE_PROBE
Use "*" to force probe the driver for all known devices.+config DRM_I915_BACKLIGHT
- tristate "Control backlight support"
- depends on DRM_I915
- default DRM_I915
- select BACKLIGHT_CLASS_DEVICE
- help
Say Y here if you want to control the backlight of your display(e.g. a laptop panel).config DRM_I915_CAPTURE_ERROR bool "Enable capturing GPU state following a hang" depends on DRM_I915 diff --git a/drivers/gpu/drm/i915/display/intel_panel.c b/drivers/gpu/drm/i915/display/intel_panel.c index 7b3ec6eb3382..e2fe7a50dcbf 100644 --- a/drivers/gpu/drm/i915/display/intel_panel.c +++ b/drivers/gpu/drm/i915/display/intel_panel.c @@ -1203,7 +1203,7 @@ void intel_panel_enable_backlight(const struct intel_crtc_state *crtc_state, mutex_unlock(&dev_priv->backlight_lock); }
-#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE) +#if IS_ENABLED(CONFIG_DRM_I915_BACKLIGHT) static u32 intel_panel_get_backlight(struct intel_connector *connector) { struct drm_i915_private *dev_priv = to_i915(connector->base.dev); @@ -1370,7 +1370,7 @@ void intel_backlight_device_unregister(struct intel_connector *connector) panel->backlight.device = NULL; } } -#endif /* CONFIG_BACKLIGHT_CLASS_DEVICE */ +#endif /* CONFIG_DRM_I915_BACKLIGHT */
/*
- CNP: PWM clock frequency is 19.2 MHz or 24 MHz.
diff --git a/drivers/gpu/drm/i915/display/intel_panel.h b/drivers/gpu/drm/i915/display/intel_panel.h index cedeea443336..e6e81268b7ed 100644 --- a/drivers/gpu/drm/i915/display/intel_panel.h +++ b/drivers/gpu/drm/i915/display/intel_panel.h @@ -49,10 +49,10 @@ intel_panel_edid_fixed_mode(struct intel_connector *connector); struct drm_display_mode * intel_panel_vbt_fixed_mode(struct intel_connector *connector);
-#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE) +#if IS_ENABLED(CONFIG_DRM_I915_BACKLIGHT) int intel_backlight_device_register(struct intel_connector *connector); void intel_backlight_device_unregister(struct intel_connector *connector); -#else /* CONFIG_BACKLIGHT_CLASS_DEVICE */ +#else /* CONFIG_DRM_I915_BACKLIGHT */ static inline int intel_backlight_device_register(struct intel_connector *connector) { return 0; @@ -60,6 +60,6 @@ static inline int intel_backlight_device_register(struct intel_connector *connec static inline void intel_backlight_device_unregister(struct intel_connector *connector) { } -#endif /* CONFIG_BACKLIGHT_CLASS_DEVICE */ +#endif /* CONFIG_DRM_I915_BACKLIGHT */
#endif /* __INTEL_PANEL_H__ */