linux-kernel - Re: [PATCH 1/3] dummycon: only build module if there are users

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Message-ID: <29ecc7c4-2887-4989-a1d3-aa76b44c0387@suse.de>
Date: Wed, 26 Feb 2025 09:16:26 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Arnd Bergmann <arnd@...db.de>, Arnd Bergmann <arnd@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Helge Deller <deller@....de>
Cc: linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dummycon: only build module if there are users

Hi

Am 26.02.25 um 08:55 schrieb Arnd Bergmann:
> On Wed, Feb 26, 2025, at 08:48, Thomas Zimmermann wrote:
>> Am 25.02.25 um 17:44 schrieb Arnd Bergmann:
>>> From: Arnd Bergmann <arnd@...db.de>
>>>
>>> Dummycon is used as a fallback conswitchp for vgacon and fbcon
>>> in the VT code, and there are no references to it if all three
>>> are disabled, so just leave it out of the kernel image for
>>> configurations without those.
>>>
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>> ---
>>>    drivers/video/console/Kconfig | 3 +--
>>>    1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
>>> index bc31db6ef7d2..1c4263c164ce 100644
>>> --- a/drivers/video/console/Kconfig
>>> +++ b/drivers/video/console/Kconfig
>>> @@ -47,8 +47,7 @@ config SGI_NEWPORT_CONSOLE
>>>    	  card of your Indy.  Most people say Y here.
>>>    
>>>    config DUMMY_CONSOLE
>>> -	bool
>>> -	default y
>>> +	def_bool VT || VGA_CONSOLE || FRAMEBUFFER_CONSOLE
>> What about MDA_CONSOLE and STI_CONSOLE. Don't they require this as fallback?
>>
> MDA_CONSOLE clearly does not, because that is only the second
> console when VGA_CONSOLE is the main one.
>
> For sti_console, I don't see how it would do use it: when CONFIG_VT
> is enabled, the line above turns on DUMMY_CONSOLE, but without
> CONFIG_VT there seems to be no reference to it after
> 58a5c67aadde ("parisc/sticon: Always register sticon console
> driver"). I also see that CONFIG_STI_CONSOLE is a 'bool' symbol,
> so there is no dynamic loading/unloading of the driver.

Thanks.

Here's another general question. vgacon and fbcon only seem usable with 
CONFIG_VT=y. Wouldn't it make sense to have them depend on CONFIG_VT=y? 
dummycon could then be implemented as part of the vt code, maybe even 
become a vt-internal thing. The console code is complex, so I'm probably 
missing something here?

Best regards
Thomas

>
>      Arnd

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)