linux-kernel - Re: [PATCH 2/2] tty: serial: 8250_core: Check that port->line is >=0

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Date:	Fri, 16 Jan 2015 12:33:09 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, monstr@...str.eu,
	Olof Johansson <olof@...om.net>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
	Peter Hurley <peter@...leysoftware.com>,
	Alan Cox <alan@...ux.intel.com>,
	Tony Lindgren <tony@...mide.com>,
	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 2/2] tty: serial: 8250_core: Check that port->line is
 >=0

On 01/16/2015 12:02 PM, Michal Simek wrote:
>>> Origin patch looks good to me but this checking will be good to add.
>>> Are you using of_serial.c because I didn't find any of_alias_get_id call
>>> for 8250?
>>
>> I'm using of_alias_get_id() in 8250_omap.c which made it into
>> v3.19-rc1. I think the change you mention made it one release earlier.
> 
> I see
> serial: of-serial: fetch line number from DT
> commit 1bd8324535ec1ff44aef55c0e40b9e7d56b310fb
> 
> but it was reverted
> 
> Revert "serial: of-serial: fetch line number from DT"
> commit e4c787dac21e50ac9ef53fac91b9182d4fede465
> 
> Olof: what was the reason for that breakage?
> Is it missing alias list on Tegra?
> which caused that port->line number is bogus.

I doubt it, because a missing alias would return -1 and would not be
considered for port->line.

I think it is more what happens if you use the second UART and the
primary is unused (as in not probed). With this change the console will
be on ttyS1 - without it it remains on ttyS0. The former is what we
wanted.

And it seems they use for "nvidia,tegra[23]0-hsuart" the serial-tegra.c
driver which makes use of of_alias_get_id() but the of_serial() one
which is used by nvidia,tegra20-uart() does not. And since this change
does not notify anyone during upgrade but removes the console everyone
gets a little grumpy*.

* and I've been looking for a smooth solution for the ttyOx -> ttySx
  change in OMAP just to avoid people complaining and risking a revert
  :)

> Thanks,
> Michal

Sebastian
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