linux-kernel - Re: [PATCH] serial: core: Use cons->index for preferred console registration

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Message-ID: <622f4c5e-e3ed-3f91-254d-78d905de79c9@xilinx.com>
Date:   Tue, 15 Oct 2019 16:36:56 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>
Cc:     Michal Simek <michal.simek@...inx.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] serial: core: Use cons->index for preferred console
 registration

On 15. 10. 19 11:51, Geert Uytterhoeven wrote:
> Hi Michal,
> 
> On Tue, Oct 15, 2019 at 11:22 AM Michal Simek <monstr@...str.eu> wrote:
>> On 15. 10. 19 11:19, Geert Uytterhoeven wrote:
>>> On Mon, Sep 2, 2019 at 4:29 PM Michal Simek <michal.simek@...inx.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@...inx.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.

ok. I will take a look at why it is not initialized in this case. Do you
have any qemu available for these boards?

Greg: Please revert this patch I will investigate why it is failing.

Thanks,
Michal