Re: [PATCH] Disable Bus Master on PCI device shutdown

[Khalid Aziz <khalid.aziz@hp.com>]

On Wed, 2012-06-06 at 14:16 -0600, Myron Stowe wrote:
> Hay Khalid,
> 
> I've been following this discussion but still do not understand what the
> perceived correct fix is for the situation you were originally trying to
> circumvent - namely, stopping NIC devices from triggering DMA activity
> upon receipt of an incoming packet.
> 
> From the discussion it sounds like a driver, upon shutdown, can end
> all active I/O
> clearing the I/O queue, and also (?) shut down its DMA engine, and may
> also go as far as disabling the Bus Master bit.
> 
> What was occurring in the original issue - was the driver in question not
> shutting down its DMA engine for some, possibly valid, reason?
> 
> Thanks,
>  Myron

Hi Myron,

The last driver issue with kexec was reported on kexec mailing list in
July of last year and that was with qla driver. From what H Peter Anvin
described, the driver left DMA engine running.

For the issue I found on an ia64 platform, it was so many years ago that
you are now taxing my old and decrepit memory :) I am digging through
old internal bug reports and will let you know once I find that original
bug report.

====================================================================
Khalid Aziz                                         Unix Systems Lab
(970)898-9214                                        Hewlett-Packard
khalid.aziz@hp.com                                  Fort Collins, CO