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Message-ID: <bb8d631d-9f6c-48e8-a504-8931ee21014d@amd.com>
Date: Thu, 15 Feb 2024 13:40:43 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Daniel van Vugt <daniel.van.vugt@...onical.com>
Cc: 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>, Maxime Ripard <mripard@...nel.org>,
linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] fbcon: Defer console takeover for splash screens
to first switch
On 2/13/2024 23:24, 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 the first switch.
I think your comment from the earlier version that this can still happen
on simpledrm (albeit less frequently) is very relevant here for the
commit message.
>
> v2: Added Kconfig option instead of hard coding "splash".
> v3: Default to disabled, not "splash". If enabled then take over on
> switch rather than on first output after switch.
>
These you'll want below the cutlist (---)
Also I think you should mention in the commit message that the
indication of a userspace splash is set by the Kconfig.
> 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 | 12 +++++++++
> drivers/video/fbdev/core/fbcon.c | 44 +++++++++++++++++++++++++++++---
> 2 files changed, 52 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> index bc31db6ef7..2f9435335f 100644
> --- a/drivers/video/console/Kconfig
> +++ b/drivers/video/console/Kconfig
> @@ -138,6 +138,18 @@ 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 "Command line parameter to defer takeover to first switch"
> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
> + default ""
> + help
> + If enabled this defers further the framebuffer console taking over
> + until the first console switch has occurred. And even then 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.
> +
> 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 1183e7a871..e5d841ab03 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"
> @@ -3348,7 +3349,7 @@ static int fbcon_output_notifier(struct notifier_block *nb,
> {
> WARN_CONSOLE_UNLOCKED();
>
> - pr_info("fbcon: Taking over console\n");
> + pr_info("fbcon: Taking over console for output\n");
>
> dummycon_unregister_output_notifier(&fbcon_output_nb);
>
> @@ -3357,6 +3358,27 @@ 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) {
> + pr_info("fbcon: Taking over console for switch\n");
> + dummycon_unregister_switch_notifier(&fbcon_switch_nb);
> + schedule_work(&fbcon_deferred_takeover_work);
> + }
> +
> + return NOTIFY_OK;
> +}
> +#endif
> #endif
Once you start adding nested #ifdef, I think it's very useful to add a
comment on the #endif to make it easier to follow the code.
IE
#endif /* CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION */
>
> static void fbcon_start(void)
> @@ -3368,8 +3390,18 @@ static void fbcon_start(void)
> deferred_takeover = false;
>
> 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
> + {
> + fbcon_output_nb.notifier_call = fbcon_output_notifier;
> + dummycon_register_output_notifier(&fbcon_output_nb);
> + }
> return;
> }
> #endif
> @@ -3416,8 +3448,12 @@ 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);
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