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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 15 Oct 2019 11:51:48 +0200
Message-ID: <CAMuHMdWZYALZB1bP5Mtoq4Nj5iubzdWBf1vRY9Mh5QvjCDhBgA@mail.gmail.com>
Subject: Re: [PATCH] serial: core: Use cons->index for preferred console registration
To:     Michal Simek <monstr@monstr.eu>
Cc:     Michal Simek <michal.simek@xilinx.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.com>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>
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Hi Michal,

On Tue, Oct 15, 2019 at 11:22 AM Michal Simek <monstr@monstr.eu> wrote:
> On 15. 10. 19 11:19, Geert Uytterhoeven wrote:
> > On Mon, Sep 2, 2019 at 4:29 PM Michal Simek <michal.simek@xilinx.com> wrote:
> >> The reason for this patch is xilinx_uartps driver which create one dynamic
> >> instance per IP with unique major and minor combinations. drv->nr is in
> >> this case all the time setup to 1. That means that uport->line is all the
> >> time setup to 0 and drv->tty_driver->name_base is doing shift in name to
> >> for example ttyPS3.
> >>
> >> register_console() is looping over console_cmdline array and looking for
> >> proper name/index combination which is in our case ttyPS/3.
> >> That's why every instance of driver needs to be registered with proper
> >> combination of name/number (ttyPS/3). Using uport->line is doing
> >> registration with ttyPS/0 which is wrong that's why proper console index
> >> should be used which is in cons->index field.
> >>
> >> Also it is visible that recording console should be done based on
> >> information about console not about the port but in most cases numbers are
> >> the same and xilinx_uartps is only one exception now.
> >>
> >> Signed-off-by: Michal Simek <michal.simek@xilinx.com>
> >
> > This is now commit 91daae03188e0dd1 ("serial: core: Use cons->index
> > for preferred console registration") in tty-next.
> >
> > This has been bisected to break the serial console on (at least)
> > r8a7791/koelsch and r8a7795/h3-salvator-xs.
> >
> > The line "printk: console [ttySC0] enabled" is no longer printed.
> > The system continues booting without any serial console output, and the
> > login prompt never appears on the serial console.
> >
> > Reverting this commit fixes the issue.
>
> Sorry for trouble with this patch. Can you please point me to dts files
> for these boards and also what's the value you have in uport->line and

arch/arm/boot/dts/r8a7791-koelsch.dts
arch/arm64/boot/dts/renesas/r8a7795-salvator-xs.dts

> uport->cons->index?

On r8a7791/koelsch:

    Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
    platform serial8250: uport->line = 0, uport->cons->index = -1
    platform serial8250: uport->line = 1, uport->cons->index = -1
    platform serial8250: uport->line = 2, uport->cons->index = -1
    platform serial8250: uport->line = 3, uport->cons->index = -1
    SuperH (H)SCI(F) driver initialized
  * sh-sci e6e60000.serial: uport->line = 0, uport->cons->index = -1
  * e6e60000.serial: ttySC0 at MMIO 0xe6e60000 (irq = 79, base_baud =
0) is a scif
    printk: console [ttySC0] enabled
    sh-sci e6e68000.serial: uport->line = 1, uport->cons->index = 0
    e6e68000.serial: ttySC1 at MMIO 0xe6e68000 (irq = 80, base_baud =
0) is a scif

On r8a7795/salvator-xs:

    sh-sci e6550000.serial: uport->line = 1, uport->cons->index = -1
    e6550000.serial: ttySC1 at MMIO 0xe6550000 (irq = 34, base_baud =
0) is a hscif
  * sh-sci e6e88000.serial: uport->line = 0, uport->cons->index = -1
  * e6e88000.serial: ttySC0 at MMIO 0xe6e88000 (irq = 120, base_baud =
0) is a scif
    printk: console [ttySC0] enabled

Actual serial consoles marked with *.

There are no 8250 serial ports in the system, shmobile_defconfig just includes
driver support for it.

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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