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Message-ID: <e4fc61ae-97f5-4fa1-bfed-1312466a2a22@amd.com>
Date: Tue, 6 Feb 2024 09:41:29 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Daniel van Vugt <daniel.van.vugt@...onical.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Helge Deller
<deller@....de>, 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 2/6/2024 08:21, Daniel Vetter wrote:
> 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).
>
IIUC there is an "automatic" VT switch that happens with Ubuntu GRUB +
Ubuntu kernels.
Why?
Couldn't this also be suppressed by just not doing that?
> 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
>>
>
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