linux-kernel - Re: [PATCH v4 2/2] fbcon: Defer console takeover for splash screens to first switch

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Message-ID: <rwifwv74dhd5dipnoi2txnecsydvfnrbog2ntk76hplf3tpdzt@5d4goejupypn>
Date: Thu, 22 Feb 2024 12:08:11 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Daniel van Vugt <daniel.van.vugt@...onical.com>
Cc: Mario Limonciello <mario.limonciello@....com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Helge Deller <deller@....de>, Daniel Vetter <daniel@...ll.ch>, 
	Thomas Hellström <thomas.hellstrom@...ux.intel.com>, Jani Nikula <jani.nikula@...el.com>, linux-fbdev@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] fbcon: Defer console takeover for splash screens
 to first switch

Hi Daniel,

On Mon, Feb 19, 2024 at 05:02:34PM +0800, Daniel van Vugt wrote:
> Until now, deferred console takeover only meant defer until there is
> output. But that risks stepping on the toes of userspace splash screens
> as console messages may appear before the splash screen.
> 
> This becomes more likely the later the splash screen starts, but even
> systems whose splash exists in initrd may not be not immune because they
> still rely on racing against all possible kernel messages that might
> trigger the fbcon takeover. And those kernel messages are hardware
> dependent so what boots silently on one machine may not be so quiet on
> the next. We also want to shield users from seeing warnings about their
> hardware/firmware that they don't always have the power to fix themselves,
> and may not be deemed worthy of fixing by the vendor.
> 
> So now we check the command line for the expectation of userspace splash
> (CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION) and if present
> then defer fbcon's takeover until the first console switch. In the case
> of Plymouth, its value would typically be "splash". This keeps the boot
> experience clean and silent so long as the command line requests so.
> 
> Closes: https://bugs.launchpad.net/bugs/1970069
> Cc: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Daniel van Vugt <daniel.van.vugt@...onical.com>

It's not clear to me why we should want to make it an option? If one
strategy is better than the other, and I guess the new one is if you
consider it fixes a bug and bothered to submit it upstream, why not just
get rid of the old one entirely?

I guess my question is: why do we want the choice, and what are the
tradeoff each strategy brings?

Maxime

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