Re: chosen/stdout-path and userland (Re: Can't boot kernel v4.0-rc2 on Koelsch)

[Peter Hurley <peter@hurleysoftware.com>]

On 03/11/2015 06:08 AM, Geert Uytterhoeven wrote:
> TL;DR
> 
> After removing the "console=" parameter from chosen/bootargs, and relying
> solely on chosen/stdout-path, Hiep-san's Linaro userland cannot find the
> console device anymore.
> 
> On Wed, Mar 11, 2015 at 7:45 AM, Laurent Pinchart
> <laurent.pinchart@ideasonboard.com> wrote:
>> On Tuesday 10 March 2015 12:32:59 Geert Uytterhoeven wrote:
>>> On Tue, Mar 10, 2015 at 10:03 AM, Cao Minh Hiep <cm-hiep@jinso.co.jp> wrote:
>>>> On 2015年03月10日 17:05, Nobuhiro Iwamatsu wrote:
>>>>> This is user land issue.
>>>>> Hiep, if you have not changed ttySCX in inittab, you will need to change.
>>>>> Could you check your inittab?
>>>>>
>>>>> --- a/inittab    2015-03-10 15:01:58.986609389 +0900
>>>>> +++ b/inittab    2015-03-10 15:00:32.132094877 +0900
>>>>> @@ -28,7 +28,7 @@
>>>>>
>>>>>   l6:6:wait:/etc/init.d/rc 6
>>>>>   # Normally not reached, but fallthrough in case of emergency.
>>>>>   z6:6:respawn:/sbin/sulogin
>>>>>
>>>>> -SC6:12345:respawn:/sbin/getty -L 38400 ttySC6
>>>>> +SC0:12345:respawn:/sbin/getty -L 38400 ttySC0
>>>>>
>>>>>   # /sbin/getty invocations for the runlevels.
>>>>>   #
>>>>>   # The "id" field MUST be the same as the last
>>>>
>>>> There is no inittab file in Linaro userland that I am using.
>>>
>>> I'm not familiar with the Linaro userland.
>>>
>>> Is there any other configuration file that contains the string "ttySC6"?
>>> Or does the Linaro userland derive it from the kernel command line?
>>> If yes, perhaps there's a newer version that does look at stdout-path
>>> instead?
>>>
>>> The goal of the stdout-path support was to have a better description in DT
>>> and automate things. So I don't think reverting the change is the proper way
>>> forward.
>>>
>>> If you can't get it to work, I think we should bring it up with the DT
>>> people first, some of which work for Linaro.
>>
>> I quite agree with that, but how should userspace know which device node in
>> /dev corresponds to the console specified in stdout-path ?
> 
> root@koelsch:~# hd /sys/firmware/devicetree/base/chosen/stdout-path
> 00000000  2f 73 65 72 69 61 6c 40  65 36 65 36 30 30 30 30  |/serial@e6e60000|
> 00000010  00                                                |.|
> 00000011
> root@koelsch:~# ls -l /sys/devices/platform/e6e60000.serial/tty
> total 0
> drwxr-xr-x 3 root root 0 Mar 11 10:50 ttySC0
> root@koelsch:~# cat /sys/devices/platform/e6e60000.serial/tty/ttySC0/dev
> 204:8
> root@koelsch:~# ls -l /dev/ttySC0
> crw------- 1 root tty 204, 8 Mar 11 10:46 /dev/ttySC0
> 
> Hence all pieces of the puzzle are available to userspace...
> Is there another way?
> 
> BTW, we also had the "/dev/console" abstraction for quite a while.
> I've just replaced "ttySC0" by "console" in my /etc/inittab, and everything
> still works fine. That's Debian (without systemd) though, so it doesn't help
> for the Linaro userland.

The tty subsystem emits the list of consoles as a space-delimited, single text
line in /sys/class/tty/console/active (alias: /sys/devices/virtual/tty/console/active).

The first console listed is the primary console.
tty0 is not resolved to its underlying tty device name.

That said, is the original reporter of this problem even interested in
upgrading their userspace, even if this is fixed in Linaro eventually?
What about other Linaro users?

I think the only reasonable course here is to continue to support
"console=" in /chosen/bootargs.

Regards,
Peter Hurley