linux-kernel - Re: [PATCH 03/11] fblog: new framebuffer kernel log dummy driver

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Date:	Mon, 13 Aug 2012 09:34:18 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	David Herrmann <dh.herrmann@...glemail.com>
CC:	linux-fbdev@...r.kernel.org,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH 03/11] fblog: new framebuffer kernel log dummy driver

On 13/08/12 00:53, David Herrmann wrote:
> Fblog displays all kernel log messages on all connected framebuffers. It
> replaces fbcon when CONFIG_VT=n is selected. Its main purpose is to debug
> boot problems by displaying the whole boot log on the screen. This patch
> provides the first dummy module-init/deinit functions.
> 
> As it uses all the font and fb functions I placed it in
> drivers/video/console. However, this means that we need to move the check
> for CONFIG_VT in Makefile/Kconfig from drivers/video into
> drivers/video/console as fblog does not depend on CONFIG_VT.
> 
> Signed-off-by: David Herrmann <dh.herrmann@...glemail.com>

Hi David,

Couple of comments below.

~Ryan

>  config VGA_CONSOLE
>  	bool "VGA text console" if EXPERT || !X86
> -	depends on !4xx && !8xx && !SPARC && !M68K && !PARISC && !FRV && !SUPERH && !BLACKFIN && !AVR32 && !MN10300 && (!ARM || ARCH_FOOTBRIDGE || ARCH_INTEGRATOR || ARCH_NETWINDER)
> +	depends on VT && !4xx && !8xx && !SPARC && !M68K && !PARISC && !FRV && !SUPERH && !BLACKFIN && !AVR32 && !MN10300 && (!ARM || ARCH_FOOTBRIDGE || ARCH_INTEGRATOR || ARCH_NETWINDER)
>  	default y
>  	help
>  	  Saying Y here will allow you to use Linux in text mode through a
> @@ -45,7 +45,7 @@ config VGACON_SOFT_SCROLLBACK_SIZE
>  	 screenfuls of scrollback buffer

You could just place all of the CONFIG_VT options inside an if VT and
then the new fblog options in the else case rather than modifying all of
the (already overly long) depends statements.

> +config FBLOG
> +	tristate "Framebuffer Kernel Log Driver"
> +	depends on !VT && FB
> +	default n

Default n is not required, all options are default n unless otherwise
specified. I don't think you need the dependency on FB either, since
this file should only get included if CONFIG_FB is set?

> +	help
> +	  This driver displays all kernel log messages on all connected
> +	  framebuffers. It is mutually exclusive with CONFIG_FRAMEBUFFER_CONSOLE
> +	  and CONFIG_VT. It was mainly created for debugging purposes when
> +	  CONFIG_VT is not selected but you still want kernel boot messages on
> +	  the screen.

Do command line options exist to specify screens to write the debug log
to? It might be a useful feature to have.

~Ryan

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