linux-kernel - Re: [PATCH v2 RESEND] PM/console: Fix the black screen issue

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Message-ID: <CAJZ5v0jazfh7A8-6werFtsQ=XOYzDioYh19p4S4v=0to2Na4Hw@mail.gmail.com>
Date: Fri, 23 May 2025 17:10:27 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: tuhaowen <tuhaowen@...ontech.com>
Cc: pavel@...nel.org, len.brown@...el.com, rafael@...nel.org, 
	huangbibo@...ontech.com, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, wangyuli@...ontech.com
Subject: Re: [PATCH v2 RESEND] PM/console: Fix the black screen issue

On Fri, May 23, 2025 at 10:57 AM tuhaowen <tuhaowen@...ontech.com> wrote:
>
> When the computer enters sleep status without a monitor
> connected, the system switches the console to the virtual
> terminal tty63(SUSPEND_CONSOLE).
>
> If a monitor is subsequently connected before waking up,
> the system skips the required VT restoration process
> during wake-up, leaving the console on tty63 instead of
> switching back to tty1.
>
> To fix this issue, a global flag vt_switch_done is introduced
> to record whether the system has successfully switched to
> the suspend console via vt_move_to_console() during suspend.
>
> If the switch was completed, vt_switch_done is set to 1.
> Later during resume, this flag is checked to ensure that
> the original console is restored properly by calling
> vt_move_to_console(orig_fgconsole, 0).
>
> This prevents scenarios where the resume logic skips console
> restoration due to incorrect detection of the console state,
> especially when a monitor is reconnected before waking up.
>
> Signed-off-by: tuhaowen <tuhaowen@...ontech.com>
> ---
> Changes in v2:
> - Added explanation in the commit message on how the issue is fixed.
> - Link to v1: https://lore.kernel.org/all/20250516034643.22355-1-tuhaowen@uniontech.com
> ---
>  kernel/power/console.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/power/console.c b/kernel/power/console.c
> index fcdf0e14a47d..832e04bf5439 100644
> --- a/kernel/power/console.c
> +++ b/kernel/power/console.c
> @@ -16,6 +16,7 @@
>  #define SUSPEND_CONSOLE        (MAX_NR_CONSOLES-1)
>
>  static int orig_fgconsole, orig_kmsg;
> +static int vt_switch_done;

Better use bool for this.

Thanks!

>
>  static DEFINE_MUTEX(vt_switch_mutex);
>
> @@ -136,15 +137,19 @@ void pm_prepare_console(void)
>         if (orig_fgconsole < 0)
>                 return;
>
> +       vt_switch_done = 1;
> +
>         orig_kmsg = vt_kmsg_redirect(SUSPEND_CONSOLE);
>         return;
>  }
>
>  void pm_restore_console(void)
>  {
> -       if (!pm_vt_switch())
> +       if (!pm_vt_switch() && !vt_switch_done)
>                 return;
>
> +       vt_switch_done = 0;
> +
>         if (orig_fgconsole >= 0) {
>                 vt_move_to_console(orig_fgconsole, 0);
>                 vt_kmsg_redirect(orig_kmsg);
> --
> 2.20.1
>