linux-kernel - Re: [PATCH 3/3] [v2] i915: fix backlight configuration issue

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Message-ID: <87r1c6h9ek.fsf@intel.com>
Date:   Wed, 27 Oct 2021 16:41:55 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Arnd Bergmann <arnd@...nel.org>, dri-devel@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-fbdev@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        Arnd Bergmann <arnd@...db.de>,
        Matthew Auld <matthew.auld@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniele Ceraolo Spurio <daniele.ceraolospurio@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] [v2] i915: fix backlight configuration issue

On Wed, 27 Oct 2021, Arnd Bergmann <arnd@...nel.org> wrote:
> From: Arnd Bergmann <arnd@...db.de>
>
> 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'
>
> Change i915 to just 'depends on' for both BACKLIGHT_CLASS_DEVICE
> and ACPI_VIDEO, which avoids a lot of the problems.
>
> Link: https://lore.kernel.org/all/20200108140227.3976563-1-arnd@arndb.de/
> Link: https://lore.kernel.org/all/20200417155553.675905-1-arnd@arndb.de/
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> This change depends on cleaning up drivers/video/fbdev to no longer
> 'select' I2C and BACKLIGHT_CLASS_DEVICE, otherwise it causes
> dependency loops.
> ---
>  drivers/gpu/drm/i915/Kconfig | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> index 84b6fc70cbf5..f427e6d50d9b 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -3,6 +3,8 @@ config DRM_I915
>  	tristate "Intel 8xx/9xx/G3x/G4x/HD Graphics"
>  	depends on DRM
>  	depends on X86 && PCI
> +	depends on ACPI_VIDEO || !ACPI
> +	depends on BACKLIGHT_CLASS_DEVICE || !BACKLIGHT_CLASS_DEVICE
>  	select INTEL_GTT
>  	select INTERVAL_TREE
>  	# we need shmfs for the swappable backing store, and in particular
> @@ -16,10 +18,6 @@ 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

The comment needs updating as well.

Other than that,

Acked-by: Jani Nikula <jani.nikula@...el.com>

on the series.

> -	select BACKLIGHT_CLASS_DEVICE if ACPI
> -	select INPUT if ACPI
> -	select ACPI_VIDEO if ACPI
> -	select ACPI_BUTTON if ACPI
>  	select SYNC_FILE
>  	select IOSF_MBI
>  	select CRC32

-- 
Jani Nikula, Intel Open Source Graphics Center