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Subject: Re: [PATCH] drm/tinydrm: add backlight dependency for ili9341
To:     Arnd Bergmann <arnd@arndb.de>, David Airlie <airlied@linux.ie>,
        David Lechner <david@lechnology.com>
Cc:     Sean Paul <seanpaul@chromium.org>, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20180709152106.990066-1-arnd@arndb.de>
From:   =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= <noralf@tronnes.org>
Message-ID: <42317727-5159-7cc2-f6a8-18c8f97b9e6e@tronnes.org>
Date:   Tue, 10 Jul 2018 17:55:20 +0200
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Den 09.07.2018 17.20, skrev Arnd Bergmann:
> This tinydrm driver fails to link without the backlight support:
>
> drivers/gpu/drm/tinydrm/ili9341.o: In function `ili9341_probe':
> ili9341.c:(.text+0x578): undefined reference to `devm_of_find_backlight'
>
> Fixes: 3fa0e8f6f960 ("drm/tinydrm: new driver for ILI9341 display panels")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   drivers/gpu/drm/tinydrm/Kconfig | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/tinydrm/Kconfig b/drivers/gpu/drm/tinydrm/Kconfig
> index 7a8008b0783f..16f4b5c91f1b 100644
> --- a/drivers/gpu/drm/tinydrm/Kconfig
> +++ b/drivers/gpu/drm/tinydrm/Kconfig
> @@ -23,6 +23,7 @@ config TINYDRM_ILI9225
>   config TINYDRM_ILI9341
>   	tristate "DRM support for ILI9341 display panels"
>   	depends on DRM_TINYDRM && SPI
> +	depends on BACKLIGHT_CLASS_DEVICE
>   	select TINYDRM_MIPI_DBI
>   	help
>   	  DRM driver for the following Ilitek ILI9341 panels:

There was some work done to make backlight optional, but I see now that
it failed to take into account the possibility of the driver being
builtin and BACKLIGHT_CLASS_DEVICE being a module.

This is from include/linux/backlight.h:

#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
struct backlight_device *of_find_backlight(struct device *dev);
struct backlight_device *devm_of_find_backlight(struct device *dev);
#else
static inline struct backlight_device *of_find_backlight(struct device *dev)
{
     return NULL;
}

static inline struct backlight_device *
devm_of_find_backlight(struct device *dev)
{
     return NULL;
}
#endif


Anyways, thanks for fixing this:
Acked-by: Noralf Trønnes <noralf@tronnes.org>

David Lechner do you apply this?

Noralf.