linux-kernel - Re: earlycon: no match?

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Date:	Tue, 5 May 2015 06:51:39 +0200
From:	Robert Schwebel <r.schwebel@...gutronix.de>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...gutronix.de
Subject: Re: earlycon: no match?

Peter,

On Mon, May 04, 2015 at 06:31:44PM -0400, Peter Hurley wrote:
> > You say it is a diagnostics message that indicates a misspelling.
> > I fail to see what is misspelled, so what does it diagnose?
> 
> Ok, so this is only about the diagnostic message, and not about some
> other failure.
> 
> I don't typically describe harmless diagnostics that didn't appear before
> as "broken", so I was having trouble believing what I was reading.
> 
> Now that I understand that this is _only_ about a diagnostic message that
> didn't appear in previous kernels, I will direct to what I have written
> previously multiple times.
> 
> Further, I would ask how _you_ would programmatically distinguish
> misspellings amongst the following console strings?
> 
> 	console=pl012,...
> 	console=_pl011,...
> 	console=pl,...
> 	console=ttyAMA0,...

Only the last line gives me output, but with the warning. All others are
misspellings but output nothing. The last one gives me a misspelling
warning, but it is the one that makes the output work.

Obviously this was not tested on an ARM device with a serial console,
because it doesn't work there.

There should be an intended variant where *nothing* is misspelled in my
oftree+kernel commandline.

In that case, the system should come up, console comes out of the serial
line and earlycon is available. Then I should not get a diagnostic
message, becasue I did everything right.

Case A: consoleo=ttyAMA0

  Result: - system boots with output on intended serial console
          - warning about having the earlycon misspelled
          - earlycon not operational, although driver supports it

Case B: console=pl011

  Result: - no output at all, because system doesn't output to its
            intented serial console.

Case C: ...?

  Are there other things I'm supposed to do in order to do it right?

So both cases A+B are not fully working as intented, right?

I'd like to fix it, but in order to do so, I want to learn how it is
actually *intended* to work.

rsc
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