linux-kernel - Re: [PATCH v2 3/7] tty/serial: convert 8250 to generic earlycon

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Date:	Mon, 9 Jun 2014 18:18:59 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Tony Luck <tony.luck@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Yinghai Lu <yinghai@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 3/7] tty/serial: convert 8250 to generic earlycon

On Mon, Jun 9, 2014 at 5:35 PM, Tony Luck <tony.luck@...il.com> wrote:
> On Mon, Jun 9, 2014 at 3:25 PM, Tony Luck <tony.luck@...il.com> wrote:
>> Linus' tree (HEAD=963649d735c8) is spitting out all sorts of garbage
>> on the serial console - as if the baud rate is being periodically set
>> to something weird, and then back to 112500.  I see over a dozen
>> blocks of junk interspersed with good output.
>
> Ah - it seems that I need to be more specific on the cmdline
>
>      console=uart8250,io,0x3f8,115200
>
> makes all the garbage disappear.
>
> Do I need to update: Documentation/ia64/serial.txt
> which has the example of "console=uart,io,0x3f8"?

It should do auto detect of the baud-rate if it is not specified which
for 8250 is just reading the baud-rate divider and calculating the
baud-rate using the uart clock. It should just reprogram the divider
with the same divider value. I don't see anything obvious why this
would have broken.

Rob
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