Re: [PATCH] PCI: Add pci shutdown ability

[Grant Grundler <grundler@parisc-linux.org>]

On Mon, Apr 25, 2005 at 04:14:13PM -0400, Alan Stern wrote:
> > Not sure what you mean by "make kexec work nicer" but if it is because
> > some devices don't work after a kexec I have some objections.
> 
> That was indeed the reason, at least in my case.  The newly-rebooted
> kernel doesn't work too well when there are active devices, with no driver
> loaded, doing DMA and issuing IRQs because they were never shut down.

This is also a problem at "normal" boot time.  BIOS may leave devices
still doing DMA if BIOS (or the arch equivalent) was using the device.
This problem is obvious for systems with an IOMMU (e.g. parisc).
See drivers/parisc/sba_iommu.c for an example of where I try to
deal with active DMA at boot time *before* PCI bus walks have occurred.
Masking IRQs is trivial in comparison to dealing with active DMA.

> > What about the kexec-on-panic?

Same problem - just much more likely to hit the issue and completely
crash the box or corrupt memory.

grant