Messages in this thread | | | Date | Tue, 10 Mar 2009 09:48:10 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 02/18] Blackfin Serial Driver: use barrier instead of cpu_relax for Blackfin SMP like patch |
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On Tue, 10 Mar 2009 06:25:08 -0400 Mike Frysinger <vapier.adi@gmail.com> wrote:
> On Tue, Mar 10, 2009 at 06:07, gyang wrote: > > On Fri, 2009-03-06 at 14:37 -0800, Andrew Morton wrote: > >> On Fri, 6 Mar 2009 14:42:44 +0800 > >> Bryan Wu <cooloney@kernel.org> wrote: > >> > >> > From: Graf Yang <graf.yang@analog.com> > >> > > >> > We are making a SMP like patch to blackfin, cpu_relax() is replaced by a > >> > data cache flush function which will count it to a per-cpu counter. > >> > If this serial function is called too early, the per-cpu data area have > >> > not been initialized, this call will cause crash. > >> > >> That's a bug in blackfin architecture support. The kernel should be > >> able to call cpu_relax() at any time, surely. It's a very low-level > >> and simple thing. > >> > >> > So we'd like to use barrier() instead of cpu_relax(). > >> > > >> > >> barrier() is purely a compiler concept. We might as well just remove > >> the cpu_relax() altogether. > > > > Do you mean remove cpu_relax(), and either not add barrier() here? > > afaik, early printk all runs before SMP is setup, so having it be a > 100% busy wait is fine
No, blackfin is busted, please fix this bug in blackfin core.
What happens if core kernel code decides to run cpu_relax() prior to initialising per-cpu data? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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