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

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Date:   Wed, 16 Mar 2022 20:31:03 +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:     Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jani Nikula <jani.nikula@...el.com>,
        Sam Ravnborg <sam@...nborg.org>,
        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>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Alex Deucher <alexander.deucher@....com>,
        Dillon Min <dillon.minfei@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: add CONFIG_DRM_KMS_HELPER dependencies



Am 16.03.22 um 20:12 schrieb Thomas Zimmermann:
> 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]

[1] 
https://lore.kernel.org/dri-devel/20220315084559.23510-1-tzimmermann@suse.de/

> 
> 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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