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

[Bill Paul <wpaul@windriver.com>]

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. :)

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

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