On Thu, 2006-05-18 at 02:34 -0700, Andrew Morton wrote: > Michael Ellerman <[email protected]> wrote: > > > > Currently printk is no use for early debugging because it refuses to actually > > print anything to the console unless cpu_online(smp_processor_id()) is true. > > > > The stated explanation is that console drivers may require per-cpu resources, > > or otherwise barf, because the system is not yet setup correctly. Fair enough. > > > > However some console drivers might be quite happy running early during boot, > > in fact we have one, and so it'd be nice if printk understood that. > > > > So I add a flag (which I would have called CON_BOOT, but that's taken) called > > CON_ANYTIME, which indicates that a console is happy to be called anytime, > > even if the cpu is not yet online. > > > > Tested on a Power 5 machine, with both a CON_ANYTIME driver and a bogus > > console driver that BUG()s if called while offline. No problems AFAICT. > > Built for i386 UP & SMP. > > hm, OK. But iirc is was just one silly ia64 console driver which had this > problem. It might be better to make the new behaviour be the default and mark > the ia64 driver CON_NEEDS_CPU_ONLINE or something. > > No? > > Or go through and audit the drivers and sprinkle CON_ANYTIME in all the > safe ones, maybe. Quite possibly, I started from the assumption that we liked the current behaviour. Inverting the logic, ie. CON_NEEDS_CPU_ONLINE, would be ok with me, but it would be a much more intrusive change. All of a sudden we'll be calling into all sorts of drivers that we didn't previously. I'll trawl through the console drivers tomorrow and see if I can guess what percentage look like they will/won't work, then we can decide which way to flip it. cheers -- Michael Ellerman IBM OzLabs wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person
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