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

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Message-Id: <a2c0e681-2cdf-4dc9-82fc-be35f54ff795@app.fastmail.com>
Date: Wed, 26 Feb 2025 08:55:14 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Thomas Zimmermann" <tzimmermann@...e.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

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.

    Arnd