On Fri, 2008-12-12 at 20:19 +0100, Arnd Bergmann wrote: > Commit d015fe995 'powerpc/cell/axon-msi: Retry on missing interrupt' > has turned a rare failure to kexec on QS22 into a reproducible > error, which we have now analysed. > > The problem is that after a kexec, the MSIC hardware still points > into the middle of the old ring buffer. We set up the ring buffer > during reboot, but not the offset into it. On older kernels, this > would cause a storm of thousands of spurious interrupts after a > kexec, which would most of the time get dropped silently. > > With the new code, we time out on each interrupt, waiting for > it to become valid. If more interrupts come in that we time > out on, this goes on indefinitely, which eventually leads to > a hard crash. > > The solution in this patch is to read the current offset from > the MSIC when reinitializing it. This now works correctly, as > expected. > > Reported-by: Dirk Herrendoerfer <d.herrendoer...@de.ibm.com> > Signed-off-by: Arnd Bergmann <a...@arndb.de> > --- > > Please apply when Dirk and Michael have given their Ack. > Should we have it in 2.6.28? Not sure if going from 'works sometimes' > to 'works never' counts as a regression. Most users won't be impacted, > because they don't use kexec on QS22.
I think it does count, it's a pretty small fix. > diff --git a/arch/powerpc/platforms/cell/axon_msi.c > b/arch/powerpc/platforms/cell/axon_msi.c > index 442cf36..548fa4e 100644 > --- a/arch/powerpc/platforms/cell/axon_msi.c > +++ b/arch/powerpc/platforms/cell/axon_msi.c > @@ -413,6 +422,9 @@ static int axon_msi_probe(struct of_device *device, > MSIC_CTRL_IRQ_ENABLE | MSIC_CTRL_ENABLE | > MSIC_CTRL_FIFO_SIZE); > > + msic->read_offset = dcr_read(msic->dcr_host, MSIC_WRITE_OFFSET_REG) > + & MSIC_FIFO_SIZE_MASK; > + Acked-by: Michael Ellerman <mich...@ellerman.id.au> cheers -- Michael Ellerman OzLabs, IBM Australia Development Lab 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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