Re: [Fastboot] Re: [RFC/PATCH] Kdump: Disabling PCI interrupts in capture kernel

[ebiederm@xmission.com (Eric W. Biederman)]

Grant Grundler <grundler@parisc-linux.org> writes:

> On Tue, Jun 07, 2005 at 12:42:42PM -0600, Eric W. Biederman wrote:
> > The howto deal with an IOMMU has been sorted out but so far no one 
> > has actually done it.  What has been discussed previously is simply
> > reserving a handful of IOMMU entries,
> 
> How? with dma_alloc_consistent() or some special hook?
> I'm just curious.

We didn't get that far but I believe the idea was a special hook.

> ...
> >  and then only using those
> > in the crash recover kernel.  This is essentially what we do with DMA
> > on architectures that don't have an IOMMU and it seems quite safe
> > enough there.
> 
> Yeah, in general that should be feasible.
> 
> One might be able to trivially allocate a small, seperate IO PDIR
> just for KDUMP and switch to that. Key thing is it be physically
> contiguous in memory. Very little code is involved with IO Pdir
> setup for both parisc and IA64. I can't speak for Alpha/sparc/ppc/et al.

Cool.
 
> ...
> > Well we are at least capable of multitasking but that is no longer the
> > primary focus.  Having polling as at least an option should make
> > debugging easier.  Last I looked Andrews kernel hand an irqpoll option
> > to do something very like this.
> 
> You could run the itimer but I don't see why you should.
> Kdump is essentially an embedded linux kernel. It really
> doesn't need to be premptive multitasking either.

It is mostly a matter of minimizing differences from the norm.

> Anyway, sounds like you guys are on the right track.

Thanks.   It just takes a while for the simple solutions to
get there.

Eric