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

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Date:	Wed, 13 Jan 2016 12:14:04 +0100
From:	Sebastian Frias <sf84@...oste.net>
To:	Peter Hurley <peter@...leysoftware.com>
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

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)

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.

>
>> NOTE: on my tree I'm using the patch I previously submitted here, so Linux is probing the UART so it works for all my cases, but I would like to go back to a standard tree.
>
> I expect that patch to go into -next sometime during the 4.5-rc cycle.

Sounds good!
Thanks,

Sebastian

>
>
> Regards,
> Peter Hurley
>
>>> Note: calling the UART driver "Au1x00/RT288x" is a bit of a misnomer,
>>> as these are names of SoCs using that distinct register layout.
>>> The actual IP is probably the 16550-compatible Palmchip BK-3103.
>>> https://sites.google.com/a/palmchiptech.com/palmchiptech/product-services/hardware-services/ip-cores/bk-3103
>>> (Not sure that this website is legitimate, though.)
>>>
>>> When I need earlyprintk support, I use this patch from Mans:
>>> http://thread.gmane.org/gmane.linux.kernel/2081016
>>>
>>> Regards.
>>>
>