linux-kernel - Re: [PATCH] drm/panel: add CONFIG_DRM_KMS

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Date:   Wed, 16 Mar 2022 20:12:41 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Arnd Bergmann <arnd@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Jani Nikula <jani.nikula@...el.com>,
        Dillon Min <dillon.minfei@...il.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        dri-devel@...ts.freedesktop.org,
        Douglas Anderson <dianders@...omium.org>,
        Deepak Rawat <drawat.floss@...il.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Alex Deucher <alexander.deucher@....com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: add CONFIG_DRM_KMS_HELPER dependencies

Hi

Am 16.03.22 um 19:36 schrieb Arnd Bergmann:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The driver fails to build when the KMS helpers are disabled:
> 
> ld.lld: error: undefined symbol: drm_gem_fb_get_obj
>>>> referenced by drm_mipi_dbi.c
>>>>                gpu/drm/drm_mipi_dbi.o:(mipi_dbi_buf_copy) in archive drivers/built-in.a
>>>> referenced by drm_mipi_dbi.c
>>>>                gpu/drm/drm_mipi_dbi.o:(mipi_dbi_fb_dirty) in archive drivers/built-in.a
> 
> ld.lld: error: undefined symbol: drm_gem_fb_begin_cpu_access
>>>> referenced by drm_mipi_dbi.c
>>>>                gpu/drm/drm_mipi_dbi.o:(mipi_dbi_buf_copy) in archive drivers/built-in.a
> 
> ld.lld: error: undefined symbol: drm_fb_swab
>>>> referenced by drm_mipi_dbi.c
>>>>                gpu/drm/drm_mipi_dbi.o:(mipi_dbi_buf_copy) in archive drivers/built-in.a
> 
> ld.lld: error: undefined symbol: drm_fb_xrgb8888_to_rgb565
>>>> referenced by drm_mipi_dbi.c
>>>>                gpu/drm/drm_mipi_dbi.o:(mipi_dbi_buf_copy) in archive drivers/built-in.a
> 
> ld.lld: error: undefined symbol: drm_fb_memcpy
>>>> referenced by drm_mipi_dbi.c
>>>>                gpu/drm/drm_mipi_dbi.o:(mipi_dbi_buf_copy) in archive drivers/built-in.a
> 
> This is fairly hard to hit in randconfig drivers, but it eventually
> did trigger for me in a configuration where all other DRM drivers
> are loadable modules, but DRM_PANEL_WIDECHIPS_WS2401 was built-in.
> 
> Adding a dependency in all drivers that select DRM_MIPI_DBI avoids
> the problem for now, adding the dependency in DRM_MIPI_DBI as well
> should help make it easier to figure out why it breaks if someone
> forgets the dependency the next time.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/gpu/drm/Kconfig       | 2 +-
>   drivers/gpu/drm/panel/Kconfig | 4 ++++
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> I see this warning on 5.17-rc8, but did not test it on linux-next,
> which may already have a fix.
> 
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index b1f22e457fd0..d5ec0b77c010 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -30,7 +30,7 @@ menuconfig DRM
>   
>   config DRM_MIPI_DBI
>   	tristate
> -	depends on DRM
> +	depends on DRM_KMS_HELPER

This symbol cannot be selected by users, so it's maybe not a good idea 
to depend on it. In fact, I've had to remove such a statement because it 
created a cyclic dependency. [1]

Making the drivers depend on KMS helpers is the right thing though. If 
there's a better solution, please let me know.

Best regards
Thomas

>   
>   config DRM_MIPI_DSI
>   	bool
> diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
> index 0aec5a10b064..96887d0efb9f 100644
> --- a/drivers/gpu/drm/panel/Kconfig
> +++ b/drivers/gpu/drm/panel/Kconfig
> @@ -425,6 +425,7 @@ config DRM_PANEL_SAMSUNG_DB7430
>   	tristate "Samsung DB7430-based DPI panels"
>   	depends on OF && SPI && GPIOLIB
>   	depends on BACKLIGHT_CLASS_DEVICE
> +	depends on DRM_KMS_HELPER
>   	select DRM_MIPI_DBI
>   	help
>   	  Say Y here if you want to enable support for the Samsung
> @@ -440,6 +441,7 @@ config DRM_PANEL_SAMSUNG_S6D16D0
>   config DRM_PANEL_SAMSUNG_S6D27A1
>   	tristate "Samsung S6D27A1 DPI panel driver"
>   	depends on OF && SPI && GPIOLIB
> +	depends on DRM_KMS_HELPER
>   	select DRM_MIPI_DBI
>   	help
>   	  Say Y here if you want to enable support for the Samsung
> @@ -476,6 +478,7 @@ config DRM_PANEL_SAMSUNG_S6E63M0_SPI
>   	depends on SPI
>   	depends on DRM_PANEL_SAMSUNG_S6E63M0
>   	default DRM_PANEL_SAMSUNG_S6E63M0
> +	depends on DRM_KMS_HELPER
>   	select DRM_MIPI_DBI
>   	help
>   	  Say Y here if you want to be able to access the Samsung
> @@ -677,6 +680,7 @@ config DRM_PANEL_WIDECHIPS_WS2401
>   	tristate "Widechips WS2401 DPI panel driver"
>   	depends on SPI && GPIOLIB
>   	depends on BACKLIGHT_CLASS_DEVICE
> +	depends on DRM_KMS_HELPER
>   	select DRM_MIPI_DBI
>   	help
>   	  Say Y here if you want to enable support for the Widechips WS2401 DPI

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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