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Message-ID: <ZcJAVSyH3gRYx3EG@phenom.ffwll.local>
Date: Tue, 6 Feb 2024 15:21:09 +0100
From: Daniel Vetter <daniel@...ll.ch>
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>,
Jani Nikula <jani.nikula@...el.com>,
Danilo Krummrich <dakr@...hat.com>, linux-fbdev@...r.kernel.org,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] fbcon: Defer console takeover for splash screens
to first switch
On Tue, Feb 06, 2024 at 06:10:51PM +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. So check the
> command line for the expectation of userspace splash and if present then
> extend the deferral until after the first switch.
>
> V2: Added Kconfig option instead of hard coding "splash".
>
> Closes: https://bugs.launchpad.net/bugs/1970069
> Cc: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Daniel van Vugt <daniel.van.vugt@...onical.com>
> ---
> drivers/video/console/Kconfig | 13 +++++++++++
> drivers/video/fbdev/core/fbcon.c | 38 ++++++++++++++++++++++++++++++--
> 2 files changed, 49 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index bc31db6ef7..a6e371bfb4 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -138,6 +138,19 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> by the firmware in place, rather then replacing the contents with a
> black screen as soon as fbcon loads.
>
> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> + string "Framebuffer Console Deferred Takeover Condition"
> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> + default "splash"
> + help
> + If enabled this defers further the framebuffer console taking over
> + until the first console switch has occurred. And even then only if
> + text has been output, and only if the specified parameter is found
> + on the command line. This ensures fbcon does not interrupt userspace
> + splash screens such as Plymouth which may be yet to start rendering
> + at the time of the first console output. "splash" is the simplest
> + distro-agnostic condition for this that Plymouth checks for.
Hm this seems a bit strange since a lot of complexity that no one needs,
also my impression is that it's rather distro specific how you want this
to work. So why not just a Kconfig option that lets you choose how much
you want to delay fbcon setup, with the following options:
- no delay at all
- dely until first output from the console (which then works for distros
which set a log-level to suppress unwanted stuff)
- delay until first vt-switch. In that case I don't think we also need to
delay for first output, since vt switch usually means you'll get first
output right away (if it's a vt terminal) or you switch to a different
graphical console (which will keep fbcon fully suppressed on the drm
side).
I think you could even reuse the existing
CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER for this, and then just
compile-time select which kind of notifier to register (well plus the
check for "splash" on the cmdline for the vt switch one I guess).
Thoughts?
Cheers, Sima
> +
> config STI_CONSOLE
> bool "STI text console"
> depends on PARISC && HAS_IOMEM
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 63af6ab034..98155d2256 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -76,6 +76,7 @@
> #include <linux/crc32.h> /* For counting font checksums */
> #include <linux/uaccess.h>
> #include <asm/irq.h>
> +#include <asm/cmdline.h>
>
> #include "fbcon.h"
> #include "fb_internal.h"
> @@ -3358,6 +3359,26 @@ static int fbcon_output_notifier(struct notifier_block *nb,
>
> return NOTIFY_OK;
> }
> +
> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> +static int initial_console;
> +static struct notifier_block fbcon_switch_nb;
> +
> +static int fbcon_switch_notifier(struct notifier_block *nb,
> + unsigned long action, void *data)
> +{
> + struct vc_data *vc = data;
> +
> + WARN_CONSOLE_UNLOCKED();
> +
> + if (vc->vc_num != initial_console) {
> + dummycon_unregister_switch_notifier(&fbcon_switch_nb);
> + dummycon_register_output_notifier(&fbcon_output_nb);
> + }
> +
> + return NOTIFY_OK;
> +}
> +#endif
> #endif
>
> static void fbcon_start(void)
> @@ -3370,7 +3391,16 @@ static void fbcon_start(void)
>
> if (deferred_takeover) {
> fbcon_output_nb.notifier_call = fbcon_output_notifier;
> - dummycon_register_output_notifier(&fbcon_output_nb);
> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> + if (cmdline_find_option_bool(boot_command_line,
> + CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) {
> + initial_console = fg_console;
> + fbcon_switch_nb.notifier_call = fbcon_switch_notifier;
> + dummycon_register_switch_notifier(&fbcon_switch_nb);
> + } else
> +#endif
> + dummycon_register_output_notifier(&fbcon_output_nb);
> +
> return;
> }
> #endif
> @@ -3417,8 +3447,12 @@ void __exit fb_console_exit(void)
> {
> #ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> console_lock();
> - if (deferred_takeover)
> + if (deferred_takeover) {
> dummycon_unregister_output_notifier(&fbcon_output_nb);
> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION
> + dummycon_unregister_switch_notifier(&fbcon_switch_nb);
> +#endif
> + }
> console_unlock();
>
> cancel_work_sync(&fbcon_deferred_takeover_work);
> --
> 2.43.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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