Re: [REGRESSION] "of: Fix premature bootconsole disable with 'stdout-path'" breaks console on tty0

[Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Hi,

On 16-03-15 18:49, Peter Hurley wrote:
> Hi Hans,
>
> On 03/16/2015 12:31 PM, Hans de Goede wrote:
>> Hi All,
>>
>> While updating my local working tree to 4.0-rc4 this morning I noticed that I no longer
>> get console / kernel messages output on the hdmi output of my ARM board / on tty0
>>
>> This is caused by:
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/of?id=2fa645cb2703d9b3786d850db815414dfeefa51d
>>
>> Reverting this commit fixes this for me.
>>
>> What is happening here is that the "add_preferred_console("stdout-path", 0, NULL);"
>> happens before the tty0 registers stopping tty0 from becoming part of the console list
>> since there already is a preferred console at that time.
>>
>> This is an undesirable behavior change caused by the commit in question, on boards
>> where there is both video output, and a serial console configured through stdout-path
>> we want to have console output on both as we do not know which of the 2 will actually
>> be hooked up by the user.
>
> I don't see this as a regression, but rather a misconfiguration.

As said it is an undesirable behavior change, whether you want to call that a regression
or not is not all that interesting. Fixing it however is important, as e.g. Fedora
ARM images rely on this behavior, both "regular" arm as well as aarch64.

> 1. Your DT indicates the stdout device is a serial console; that is
>     the expected outcome. Here's what ePAPR has to say on the chosen/stdout-path
>     property node:
>
>     "A string that specifies the full path to the node representing the device to be
>     used for boot console output. If the character ":" is present in the value it
>     terminates the path. The value may be an alias."
>
>     If the serial console is not the stdout device then the DT should not
>     claim it is.
>
> 2. The tty0 console is not now, and has never been, always enabled.
>
>     The tty0 console is only enabled when either,
>       a) there is no other console
>       b) when specified on the command line (ie., "console=tty0") or
>          by prom/dt.
>
>     Your situation is akin to adding the serial console to the command line; if
>     "console=tty0" is not also explicitly added, there is no boot console output
>     to tty0.
>
> 3. This same breakage will happen if any other device registers a console matching
>     the stdout-path at console_init() time (ie, with console_initcall() macro) before
>     the dummy console. The order in which consoles are inited via console_initcall()
>     is dependent on link order, so essentially not controllable across different
>     subsystems (or if there were consoles defined with the arch itself).
>
> That said, I'll look into fixing your use-case automagically without requiring
> configuration changes.

Thanks!

Regards,

Hans
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