linux-kernel - Re: serial console on rb532 disabled on boot (linux 3.15rc5)

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Message-ID: <CAMuHMdUZuwA45-m8HL8PXDMXrrhp2DA71P5-jLwke0i5TLFSYw@mail.gmail.com>
Date:	Tue, 20 May 2014 10:41:15 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Waldemar Brodkorb <wbx@...nadk.org>
Cc:	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: serial console on rb532 disabled on boot (linux 3.15rc5)

Hi Waldemar,

On Tue, May 20, 2014 at 10:21 AM, Waldemar Brodkorb <wbx@...nadk.org> wrote:
> Geert Uytterhoeven wrote,
>> On Fri, May 16, 2014 at 3:49 PM, Waldemar Brodkorb <wbx@...nadk.org> wrote:
>> > I am trying to bootup my Mikrotik RB532 board with the latest
>> > kernel, but my serial console is disabled after boot:
>> > ..
>> > Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
>> > serial8250: ttyS0 at MMIO 0x0 (irq = 104, base_baud = 12499875) is a
>> > 16550A
>> > console [ttyS0] enabled
>> > console [ttyS0] disabled
>> >
>> > I used git bisect to find the problematic commit:
>> > commit 5f5c9ae56c38942623f69c3e6dc6ec78e4da2076
>> > Author: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
>> > Date:   Fri Feb 28 14:21:32 2014 +0100
>> >
>> >     serial_core: Unregister console in uart_remove_one_port()
>> >
>> >     If the serial port being removed is used as a console, it must
>> > also be
>> >     unregistered from the console subsystem using
>> > unregister_console().
>> >
>> >     uart_ops.release_port() will release resources (e.g. iounmap()
>> > the serial
>> >     port registers), causing a crash on subsequent kernel output if
>> > the console
>> >     is still registered.
>> >
>> >     Signed-off-by: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
>> >     Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> >
>> > After reverting the change, everything is fine.
>>
>> Does this patch help? https://lkml.org/lkml/2014/5/10/9
>
> The second change in printk.c didn't help.

>> Your serial driver may need to set port.type too, if it doesn't already do so
>> and the type is PORT_UNKNOWN on re-registration.
>
> Tried following patch, but it didn't work:
>
> diff -Nur linux-3.15-rc5.orig/arch/mips/rb532/serial.c
> linux-3.15-rc5/arch/mips/rb532/serial.c
> --- linux-3.15-rc5.orig/arch/mips/rb532/serial.c        2014-05-09
> 22:10:52.000000000 +0200
> +++ linux-3.15-rc5/arch/mips/rb532/serial.c     2014-05-19
> 20:35:08.000000000 +0200
> @@ -37,7 +37,7 @@
>  extern unsigned int idt_cpu_freq;
>
>  static struct uart_port rb532_uart = {
> -       .flags = UPF_BOOT_AUTOCONF,
> +       .type = PORT_16550A,

I'm afraid this is not gonna help. When the port is unregistered, its
type will be reset to PORT_UNKNOWN.
So before registering it again, its type must be set againin the actual
serial driver, cfr. the change to of_serial.c.

>         .line = 0,
>         .irq = UART0_IRQ,
>         .iotype = UPIO_MEM,
> diff -Nur linux-3.15-rc5.orig/kernel/printk/printk.c
> linux-3.15-rc5/kernel/printk/printk.c
> --- linux-3.15-rc5.orig/kernel/printk/printk.c  2014-05-09
> 22:10:52.000000000 +0200
> +++ linux-3.15-rc5/kernel/printk/printk.c       2014-05-20
> 09:39:54.000000000 +0200
> @@ -2413,6 +2413,7 @@
>         if (console_drivers != NULL && console->flags & CON_CONSDEV)
>                 console_drivers->flags |= CON_CONSDEV;
>
> +       console->flags &= ~CON_ENABLED;
>         console_unlock();
>         console_sysfs_notify();
>         return res;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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