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From:   Lukasz Majczak <lma@semihalf.com>
Date:   Thu, 2 Mar 2023 17:43:28 +0100
Message-ID: <CAFJ_xbrK9pGh_5muDKCCPz1gvaue7sKKELJfZ6TZHCU+gibtYg@mail.gmail.com>
Subject: Re: [PATCH] serial: core: fix broken console after suspend
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Jiri Slaby <jirislaby@kernel.org>,
        Guenter Roeck <groeck@chromium.org>,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        upstream@semihalf.com, stable@vger.kernel.org
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=C5=9Br., 1 mar 2023 o 15:09 Lukasz Majczak <lma@semihalf.com> napisa=C5=82=
(a):
>
> =C5=9Br., 1 mar 2023 o 13:22 Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> napisa=C5=82(a):
> >
> > On Wed, Mar 01, 2023 at 10:51:31AM +0100, Lukasz Majczak wrote:
> > > =C5=9Br., 1 mar 2023 o 09:39 Greg Kroah-Hartman
> > > <gregkh@linuxfoundation.org> napisa=C5=82(a):
> > > >
> > > > On Wed, Mar 01, 2023 at 08:57:51AM +0100, Lukasz Majczak wrote:
> > > > > Re-enable the console device after suspending, causes its cflags,
> > > > > ispeed and ospeed to be set anew, basing on the values stored in
> > > > > uport->cons. The issue is that these values are set only once,
> > > > > when parsing console parameters after boot (see uart_set_options(=
)),
> > > > > next after configuring a port in uart_port_startup() these parame=
teres
> > > > > (cflags, ispeed and ospeed) are copied to termios structure and
> > > > > the orginal one (stored in uport->cons) are cleared, but there is=
 no place
> > > > > in code where those fields are checked against 0.
> > > > > When kernel calls uart_resume_port() and setups console, it copie=
s cflags,
> > > > > ispeed and ospeed values from uart->cons,but those are alread cle=
ared.
> > > > > The efect is that console is broken.
> > > > > This patch address this by preserving the cflags, ispeed and
> > > > > ospeed fields in uart->cons during uart_port_startup().
> > > > >
> > > > > Signed-off-by: Lukasz Majczak <lma@semihalf.com>
> > > > > Cc: stable@vger.kernel.org
> > > > > ---
> > > > >  drivers/tty/serial/serial_core.c | 3 ---
> > > > >  1 file changed, 3 deletions(-)
> > > > >
> > > > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/seria=
l/serial_core.c
> > > > > index 2bd32c8ece39..394a05c09d87 100644
> > > > > --- a/drivers/tty/serial/serial_core.c
> > > > > +++ b/drivers/tty/serial/serial_core.c
> > > > > @@ -225,9 +225,6 @@ static int uart_port_startup(struct tty_struc=
t *tty, struct uart_state *state,
> > > > >                       tty->termios.c_cflag =3D uport->cons->cflag=
;
> > > > >                       tty->termios.c_ispeed =3D uport->cons->ispe=
ed;
> > > > >                       tty->termios.c_ospeed =3D uport->cons->ospe=
ed;
> > > > > -                     uport->cons->cflag =3D 0;
> > > > > -                     uport->cons->ispeed =3D 0;
> > > > > -                     uport->cons->ospeed =3D 0;
> > > > >               }
> > > > >               /*
> > > > >                * Initialise the hardware port settings.
> > > > > --
> > > > > 2.39.2.722.g9855ee24e9-goog
> > > > >
> > > >
> > > > What commit id does this fix?
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > > Hi Greg,
> > >
> > > There are actually two commits that introduce problematic uport flags
> > > clearing in uart_startup (for the sake of simplicity I'd ignore the
> > > older history):
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co=
mmit/?h=3Dv6.2&id=3Dc7d7abff40c27f82fe78b1091ab3fad69b2546f9
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co=
mmit/?h=3Dv6.2&id=3D027b57170bf8bb6999a28e4a5f3d78bf1db0f90c
> > > It's 10 years between those 2 and to me it was hard to decide about
> > > picking a proper one for the `Fixes:` tag.
> > > How would you recommend to proceed wrt applying this patch on the
> > > stable releases?
> >
> > Where do you think this needs to go to?  Pick something?
> >
> > And as you have obviously found this on a device running an older kerne=
l
> > version, what kernel tree(s) did you test it on?
> >
> > thanks,
> >
> > greg k-h
>
> As this patch applies without conflict on 4.14, I would suggest 4.14+.
> I have tested the patch on chromes-5.15 (cannonlake device).
>
> Best regards,
> Lukasz

I have tested my patch also with 4.14 and 6.1 (again chromeos tree).
On 4.14 it fixed the issue, but on 6.1 although the console survived
the suspend/resume,
it is printing different characters than requested - I will try to
debug it further.

Best regards
Lukasz