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

From: Sebastian Frias
Date: Wed Jan 13 2016 - 06:14:17 EST

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!


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.
(Not sure that this website is legitimate, though.)

When I need earlyprintk support, I use this patch from Mans: