linux-kernel - Re: post 3.14 serial regression

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Date:	Tue, 08 Apr 2014 14:38:31 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Dave Hansen <dave@...1.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org, jslaby@...e.cz
Subject: Re: post 3.14 serial regression

On 04/08/2014 02:03 PM, Dave Hansen wrote:
> On 04/08/2014 04:27 AM, One Thousand Gnomes wrote:
>>> At the end, you can see that init is somehow dying.  If I revert this
>>> patch, init is happy again and doesn't die, and the serial console works
>>> like before.
>>
>> Can you check if init is getting a SIGHUP - possibly its opening the
>> device and when it goes away gets a hangup which it isn't catching ?
> 
> I do see plenty of SIGCHLDs and a heap of SIGTERMs to 'systemd-udevd',
> but no SIGHUP.  I do see a "Warning: unable to open an initial console."
> now, though.  (details far below)
> 
> I instrumented uart_remove_one_port().  It *looks* like while searching
> for a uart_port for 0x1008 (my actual port),
> serial8250_find_match_or_unused() finds 0x3e8 since 0x3e8 is
> PORT_UNKNOWN.  The new code unregisters the 0x1008 console since it
> _thinks_ it is about to re-register it.

<sigh>

Looks like this just changed the detection order so my device went from
ttyS2 to ttyS4:

# cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:0 rx:0 CTS|DSR|CD
1: uart:16550A port:000002F8 irq:3 tx:0 rx:0
2: uart:unknown port:000003E8 irq:4
3: uart:unknown port:000002E8 irq:3
4: uart:ST16650V2 port:00001008 irq:18 tx:0 rx:0
5: uart:ST16650V2 port:00001000 irq:19 tx:0 rx:0


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