[v3,2/2] fbcon: Defer console takeover for splash screens to first switch
Commit Message
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.
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.
Closes: https://bugs.launchpad.net/bugs/1970069
Cc: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Daniel van Vugt <daniel.van.vugt@canonical.com>
---
drivers/video/console/Kconfig | 12 +++++++++
drivers/video/fbdev/core/fbcon.c | 44 +++++++++++++++++++++++++++++---
2 files changed, 52 insertions(+), 4 deletions(-)
Comments
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@amd.com>
> Signed-off-by: Daniel van Vugt <daniel.van.vugt@canonical.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);
@@ -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
@@ -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
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);