Re: [Qemu-devel] [PATCH] e1000: make ICS write-only

[Michael S. Tsirkin]

On Wed, Jan 09, 2013 at 02:21:50PM -0800, Bill Paul wrote:
> Of all the gin joints in all the towns in all the world, Michael S. Tsirkin 
> had to walk into mine at 14:07:53 on Wednesday 09 January 2013 and say:
> 
> > On Wed, Jan 09, 2013 at 01:50:39PM -0600, Anthony Liguori wrote:
> > > I figured this would be the case but this is where a comment in the code
> > > or commit message would have helped a lot in avoiding future confusion.
> > > 
> > > Regards,
> > > 
> > > Anthony Liguori
> > 
> > I just sent a documentation patch, please take a look.
> > Thanks!
> 
> Well, strictly speaking, VxWorks doesn't rely on the ICS behavior anymore, 
> but 
> it prefers it. I ran into problems with VMware and Simics too, as they also 
> don't emulate the ICS behavior, and getting that fixed was more of an uphill 
> battle. So as a compromise I added a check to the driver to see if the ICS 
> register has 'real hardware behavior' or 'emulated behavior' and made it use 
> an alternate interrupt handling scheme in the emulated case. The alternate 
> scheme is a little less efficient than the ICS scheme in some cases (mainly 
> when the PRO/1000 device's interrupt is shared), but it still handles 
> interrupts reliably.
> 
> That's a minor nit though. I'm fine with the comments as is. I just didn't 
> want you do think VxWorks was completely brain damaged. :)

I guess I'll change it to
"The VxWorks PRO/1000 driver uses this behaviour."

> Note that I don't think VMware emulates the 'flexible RX mode' descriptor 
> mechanism for the PRO/100 either, because the non-NDAed PRO/100 manual 
> doesn't 
> bother to mention it exists. I think this is something that was fixed in QEMU 
> but I haven't had a chance to test it in a while. There's a similar problem 
> with simulated the AMD PCnet/PCI devices (they only support the 
> 'configuration 
> block' setup method -- for the older non-PCI LANCE chips that was the only 
> way 
> to configure them but PCI devices starting with the am97c970 can be 
> configured 
> just by setting up registers).
> 
> Honestly I'm surprised I still have all my hair and that it's still the same 
> color.
> 
> -Bill

Yes virtio is much easier. All bugs there are our own.


> -- 
> =============================================================================
> -Bill Paul            (510) 749-2329 | Member of Technical Staff,
>                  address@hidden | Master of Unix-Fu - Wind River Systems
> =============================================================================
>    "I put a dollar in a change machine. Nothing changed." - George Carlin
> =============================================================================