linux-kernel - Re: [RFC PATCH] always probe UART HW when options are not specified

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Message-ID: <56967C7F.4060705@hurleysoftware.com>
Date:	Wed, 13 Jan 2016 08:34:07 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Sebastian Frias <sf84@...oste.net>
Cc:	Mason <slash.tmp@...e.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Mans Rullgard <mans@...sr.com>
Subject: Re: [RFC PATCH] always probe UART HW when options are not specified

On 01/13/2016 03:14 AM, Sebastian Frias wrote:
> Hi Peter,
> 
> On 01/12/2016 08:47 PM, Peter Hurley wrote:
>> On 01/12/2016 06:22 AM, Sebastian Frias wrote:
>>>
>>> For the record, I'm using a SoC emulator, and thus do not have a bootloader per se and there are a bunch of other things that I cannot count on.
>>> The emulator has the UART pre-setup, so I just need Linux to take over without changing the parameters.
>>> Ideally, I would like to have the same image of Linux+DT to start in any instance of the emulator or real chips, regardless of the clock ratios, that's why I sort of need Linux to not change the UART speed, which is quite tricky because there are no clock generators in the emulator.
>>
>> Got it, thanks for the info.
>> Please test the series I just cc'd you on plus the patch I sent
>> you yesterday.
>>
>> That should get you an earlycon up and running on that simulator;
>> let me know if it doesn't and we'll go from there.
> 
> Ok, thanks.
> I will try as soon as we finish rebasing our changes on top of
> "mainline" (or HEAD, or is it "-next"? I don't know how you guys call
> the most recent code base for Linux)

The basic tree organization is

   Linus's tree  <---- linux-next[date]  <----- maintainers' trees
   (mainline)          (next)                   (eg., Greg's tty tree)

The patches I sent you (along with any required modifications during the
review cycle) are based on the tty-next branch in Greg's tty tree here
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git

As of this email, Greg's tree is based on Linus's 4.4-rc6 which should
be stable enough for you to test these patches on.

> Actually, I tried yesterday on a 4.1.13 but
> "[drivers/tty/serial/earlycon.c:62] earlycon_map()" was still the
> last message I got, just as with the OF_EARLYCON_DECLARE hack I had
> previously talk about, and so I would like to test on the same
> conditions than you, mainline.

So just to confirm, you applied "8250: Add Au1x00/RT288x earlycon support"
to 4.1.13 and the earlycon didn't come up when you used the kernel
command line option like so:

	earlycon=rt288x,mmio32,0x10700

Is that correct?