Subject: Re: [PATCH v3] console: use first console if stdout-path device
 doesn't appear
To: Paul Burton <paul.burton@imgtec.com>,
        Michael Ellerman <mpe@ellerman.id.au>
References: <2c67e39b-fc33-918a-774e-d9238e837c03@lwfinger.net>
 <20161103125758.3415-1-paul.burton@imgtec.com>
 <8737j3n18r.fsf@concordia.ellerman.id.au> <13471233.iqSeGS5aQ3@np-p-burton>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Andreas Schwab <schwab@linux-m68k.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Borislav Petkov <bp@suse.de>, Petr Mladek <pmladek@suse.com>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
From: Larry Finger <Larry.Finger@lwfinger.net>
Message-ID: <4f990791-ebff-dbe3-b923-3cac5fd6f97d@lwfinger.net>
Date: Mon, 7 Nov 2016 09:26:37 -0600
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On 11/07/2016 03:18 AM, Paul Burton wrote:
> On Monday, 7 November 2016 19:27:32 GMT Michael Ellerman wrote:
>> Paul Burton <paul.burton@imgtec.com> writes:
>>> If a device tree specified a preferred device for kernel console output
>>> via the stdout-path or linux,stdout-path chosen node properties there's
>>> no guarantee that it will have specified a device for which we have a
>>> driver. It may also be the case that we do have a driver but it doesn't
>>> call of_console_check() to register as a preferred console (eg. offb
>>> driver as used on powermac systems).
>>>
>>> In these cases try to ensure that we provide some console output by
>>> enabling the first usable registered console, which we keep track of
>>> with the of_fallback_console variable. Affected systems will enable
>>> their console later than they did prior to commit 05fd007e4629
>>> ("console: don't prefer first registered if DT specifies stdout-path")
>>> but should otherwise produce the same output.
>>>
>>> Tested in QEMU with a PowerPC pseries_defconfig kernel.
>>
>> Hi Paul,
>>
>> This does "work", as in it boots and I get a console. But the delay in
>> getting output on the VGA is not workable. I get pretty much no output
>> until the machine is booted entirely to userspace, meaning any crash
>> prior to that will be undebuggable.
>>
>> I also note Andreas reports it doesn't work at all on PowerMac.
>>
>> Please send a revert and we can try again next cycle.
>>
>> cheers
>
> Hi Michael,
>
> A revert was already submitted by Hans de Goede & is being discussed over
> here:
>
> https://marc.info/?l=linux-kernel&m=147826151427455&w=2

I am a little surprised that I was not CCd on that thread. To reiterate, my 
PowerBook G4 with a PPC32 processor CRASHES on boot. That is a lot more serious 
than the console output disappearing.

As it seems unlikely that this regression will be fixed in the current cycle, I 
recommend that the reversion of commit 05fd007e4629 until a proper fix is available.

Larry