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

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Message-ID: <CAJZ5v0gOa8H-yABSepfy-WyOKJqRjCMhYPdbAHox3qUVmOXS6w@mail.gmail.com>
Date: Fri, 16 May 2025 10:16:34 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: tuhaowen <tuhaowen@...ontech.com>
Cc: pavel@...nel.org, len.brown@...el.com, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, huangbibo@...ontech.com, wangyuli@...ontech.com
Subject: Re: [PATCH] PM/console: Fix the black screen issue

On Fri, May 16, 2025 at 5:47 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.

Please add some information here on how exactly the issue is being
fixed.  Reverse-engineering code changes is hard.

> Signed-off-by: tuhaowen <tuhaowen@...ontech.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;
>
>  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);
> --