Re: [PATCH] drm/fb: Fix randconfig builds

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 16 Aug 2021, Jackie Liu <liu.yun@linux.dev> wrote:
> Hi Jani.
>
> My CI report an randconfigs build failed. there are:
>
> drm_fb_helper.c:(.text+0x302): undefined reference to `fb_set_suspend'
> drm_fb_helper.c:(.text+0xaea): undefined reference to `register_framebuffer'
> drm_fb_helper.c:(.text+0x1dcc): undefined reference to `framebuffer_alloc'
> ld: drm_fb_helper.c:(.text+0x1dea): undefined reference to `fb_alloc_cmap'
> ld: drm_fb_helper.c:(.text+0x1e2f): undefined reference to `fb_dealloc_cmap'
> ld: drm_fb_helper.c:(.text+0x1e5b): undefined reference to 
> `framebuffer_release'
> drm_fb_helper.c:(.text+0x1e85): undefined reference to 
> `unregister_framebuffer'
> drm_fb_helper.c:(.text+0x1ee9): undefined reference to `fb_dealloc_cmap'
> ld: drm_fb_helper.c:(.text+0x1ef0): undefined reference to 
> `framebuffer_release'
> drm_fb_helper.c:(.text+0x1f96): undefined reference to 
> `fb_deferred_io_cleanup'
> drm_fb_helper.c:(.text+0x203b): undefined reference to `fb_sys_read'
> drm_fb_helper.c:(.text+0x2051): undefined reference to `fb_sys_write'
> drm_fb_helper.c:(.text+0x208d): undefined reference to `sys_fillrect'
> drm_fb_helper.c:(.text+0x20bb): undefined reference to `sys_copyarea'
> drm_fb_helper.c:(.text+0x20e9): undefined reference to `sys_imageblit'
> drm_fb_helper.c:(.text+0x2117): undefined reference to `cfb_fillrect'
> drm_fb_helper.c:(.text+0x2172): undefined reference to `cfb_copyarea'
> drm_fb_helper.c:(.text+0x21cd): undefined reference to `cfb_imageblit'
> drm_fb_helper.c:(.text+0x2233): undefined reference to `fb_set_suspend'
> drm_fb_helper.c:(.text+0x22b0): undefined reference to `fb_set_suspend'
> drm_fb_helper.c:(.text+0x250f): undefined reference to `fb_deferred_io_init'
>
> The main reason is because DRM_FBDEV_EMULATION is built-in, and
> CONFIG_FB is compiled as a module.

DRM_FBDEV_EMULATION is not a module, it's just a config
knob. drm_fb_helper.ko is the module, enabled via DRM_KMS_HELPER, and it
has an implicit dependency on FB, and DRM_FBDEV_EMULATION selects
DRM_KMS_HELPER. Select just breaks dependencies in all kinds of ways.

This might help in config DRM_KMS_HELPER, and it might help the reader
because it's factual:

	depends on FB if DRM_FBDEV_EMULATION


BR,
Jani.





>
> --
> Jackie Liu
>
> 在 2021/8/16 下午3:01, Jani Nikula 写道:
>> On Mon, 16 Aug 2021, Jackie Liu <liu.yun@linux.dev> wrote:
>>> From: Jackie Liu <liuyun01@kylinos.cn>
>>>
>>> When CONFIG_DRM_FBDEV_EMULATION is compiled to y and CONFIG_FB is m, the
>>> compilation will fail. we need make that dependency explicit.
>> 
>> What's the failure mode? Using select here is a bad idea.
>> 
>> BR,
>> Jani.
>> 
>>>
>>> Reported-by: k2ci <kernel-bot@kylinos.cn>
>>> Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
>>> ---
>>>   drivers/gpu/drm/Kconfig | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
>>> index 7ff89690a976..346a518b5119 100644
>>> --- a/drivers/gpu/drm/Kconfig
>>> +++ b/drivers/gpu/drm/Kconfig
>>> @@ -98,7 +98,7 @@ config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
>>>   config DRM_FBDEV_EMULATION
>>>   	bool "Enable legacy fbdev support for your modesetting driver"
>>>   	depends on DRM
>>> -	depends on FB
>>> +	select FB
>>>   	select DRM_KMS_HELPER
>>>   	select FB_CFB_FILLRECT
>>>   	select FB_CFB_COPYAREA
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center