Messages in this thread | | | Subject | Re: [BK PATCH] console changes 1 | From | Andi Kleen <> | Date | 14 Oct 2002 03:18:12 +0200 |
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Andrew Morton <akpm@digeo.com> writes:
> I think what we need James is just the low-level hook in printk.c which > the various platforms and boards can plug into. The one in Martin's > patch (module some cleanups, docco, conversion to C, etc) looks > suitable to me. The actual early console drivers don't appear to have > much relationship at all to the console layer really. They're just > minimal-code busy-wait port banging.
The hook already exists and it is called register_console. Has been there for years. early_printk on x86-64 uses that. Originally I used the hackish printk hook way, but Linus put me on the right track.
Your arch code just does a register_console very early which does the low level output.
Actually you need one new hook for cosmetic reason: when the real console starts you want to disable the early console, otherwise you get duplicated output when they go to the same output device. This can be done with a straight forward function call in console_init.
BTW the x86-64 early console should just work fine on i386 too, with minor changes.
All you need to do is:
- cp arch/x86_64/kernel/early_printk.c arch/i386/kernel/early_printk.c - edit arch/i386/kernel/early_printk.c and replace VGABASE with __PAGE_OFFSET+0xb8000 - add it to arch/i386/kernel/Makefile - (optional - if you don't do it will be only initialised after setup_arch when __setup arguments are parsed) add something like if (c == ' ' && !memcmp(from,"earlyprintk=",12)) { extern int setup_early_printk(char *opt) setup_early_printk(from+12); } to the comand line parsing in arch/i386/kernel/setup.c - Enable CONFIG_EARLY_PRINTK so that console_init disables it. - Boot with earlyprintk=vga (for vga output) or earlyprintk=serial,ttySx,baud for serial output. Add ,keep when you want to keep it even after console_init
-Andi
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