ARM, earlyconsole and io mapping

Hi,

I was wondering how the earlyconsole was supposed to work in order to add support to the pxa architecture. More specifically, I don't understand how the memory mapping is supposed to be available at the early parameters parsing.

The thing I don't understand is that :
- in kernel initialization, parse_early_param() is called before machine_desc->map_io()
- as a consequence, the architecture didn't add the vm early mapping for serial peripheral (which is added in pxa_map_io())
- as a consequence, earlycon_map() will fail to map the serial MMIO (as in stack showed in [1])

Therefore, are there non-DT earlycon users on the list, and could they tell me what way they get earlycon support in their arm boards please ?

Cheers.

Robert

[1] Call stack
#0  __arm_ioremap_pfn_caller (pfn=262400, offset=0, size=64, mtype=0, caller=0xc041d66c) at arch/arm/mm/ioremap.c:260
#1  0xc0015d34 in __arm_ioremap_caller (phys_addr=<value optimized out>, size=<value optimized out>, mtype=0, caller=<value optimized out>) at arch/arm/mm/ioremap.c:354
#2  0xc0015868 in __arm_ioremap (phys_addr=<value optimized out>, size=<value optimized out>, mtype=<value optimized out>) at arch/arm/mm/ioremap.c:383
#3  0xc041d66c in earlycon_map (buf=0x0, match=0x0, setup=0x40) at drivers/tty/serial/earlycon.c:48
#4  setup_earlycon (buf=0x0, match=0x0, setup=0x40) at drivers/tty/serial/earlycon.c:138
#5  0xc040a52c in do_early_param (param=0xc0424bf6 "earlycon", val=0xc0424bff "pxa,mmio,0x40100000,115200n8", unused=<value optimized out>) at init/main.c:420
#6  0xc00306bc in parse_one (doing=0xc0393668 "early options", args=0xc0424c1b "", params=<value optimized out>, num=<value optimized out>, min_level=0, max_level=0, unknown=0) at kernel/params.c:131
#7  parse_args (doing=0xc0393668 "early options", args=0xc0424c1b "", params=<value optimized out>, num=<value optimized out>, min_level=0, max_level=0, unknown=0) at kernel/params.c:216
#8  0xc040a854 in parse_early_options (cmdline=<value optimized out>) at init/main.c:430
#9  0xc040a890 in parse_early_param () at init/main.c:444
#10 0xc040d950 in setup_arch (cmdline_p=0xc07f3fd4) at arch/arm/kernel/setup.c:922
#11 0xc040a918 in start_kernel () at init/main.c:520
  => Here get_vm_area_caller() will fail in __arm_ioremap_pfn_caller().

Dear Robert Jarzmik,

A very early mapping of the I/O space is done in head.S, way before you get into C code:

http://lxr.free-electrons.com/source/arch/arm/kernel/head.S#L277

Best regards,

Thomas

Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

That's DEBUG_LL, right ? If that's what you mean, then I already have DEBUG_LL, but that doesn't answer my question, as DEBUG_LL stops spitting logs after the decompressor, and the errors I want to trap are between end of decompressor and drivers probe.

And my question about earlycon remains, DEBUG_LL is not earlycon.

Cheers.

Robert

Hi Robert,

Fixmap support has not been upstreamed yet, but if you're desperate, here's the latest patch version:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/318372.html

If you're using /chosen/stdout-path, earlycon gets turned off at dummy VT console load, so for right now, specify your earlycon and consoles on the command line.

Regards,
Peter Hurley

Ah I'm not desperate, that would be nice to have tool on my automation platform. I've gone the DEBUG_LL + JTAG/__log_buf memory dump so far.

And yet I remember viewing early concole patches a few monthes back, and I wondered how the authors could make them work ... And as my memory didn't serve me well, I couldn't remember your name.

Ah I'm using device-tree in only 1/3rd of the PXA tests :
- 1/3rd for legacy platform_data tests
- 1/3rd for device-tree pxa platforms
- 1/3rd for multiplatform kernel

Anyway, I hope you'll have Russell's comments addressed, and that your patch will make it upstream. Thanks for the information, it is exactly what I was asking for.

Cheers.

Robert