On 01/12/2016 10:37 AM, Mason wrote:

On 11/01/2016 20:06, Peter Hurley wrote:

quoted

I don't have enough information to suggest what you "should" use
here.

Is this going to be a shipping product?
Is it single-core?
etc.

And what is your purpose for outputting early boot information
before loading the serial driver which does provide console output?

I'm not sure exactly which board Sebastian has in mind, but I've been
using the SERIAL_8250_RT288X driver on my Tango4 board.

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.

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.

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.