linux-kernel - Re: [PATCH v3] console: use first console if stdout-path device doesn't appear

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Date:   Mon, 7 Nov 2016 09:26:37 -0600
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Paul Burton <paul.burton@...tec.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andreas Schwab <schwab@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>, Petr Mladek <pmladek@...e.com>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3] console: use first console if stdout-path device
 doesn't appear

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@...tec.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