Re: [Qemu-devel] [PATCH v3] Add DSDT node for AppleSMC

[Michael S. Tsirkin]

On Wed, Dec 25, 2013 at 08:11:56PM +0100, Alexander Graf wrote:
> 
> 
> > Am 23.12.2013 um 04:19 schrieb "Gabriel L. Somlo" <address@hidden>:
> > 
> > On Sun, Dec 22, 2013 at 11:21:00PM +0100, Laszlo Ersek wrote:
> >>>    2. Use "IRQNoFlags() { 5 }" with the SMC (or any other
> >>>       number that isn't already allocated.
> >> 
> >> I don't think there's anything left free:
> >> ...
> >> 
> >> I guess the "by the book" solution would be to really stop the FDC from
> >> being emulated when the AppleSMC is present, but I mention that idea
> >> only because I like to waste bandwidth.
> >> 
> >> Option 1 ("Do nothing") sounds appropriate to me.
> > 
> > So making the FDC optional (or at least allowing it to be left out)
> > sounds like it could be a fun project I could play with later (unless
> > anyone else beats me to it), but it would be nice if it didn't end up
> > a hard precondition for getting the SMC ACPI patch accepted :)
> > 
> > Once we can turn off the FDC, we can make it and the SMC mutually
> > exclusive and/or throw an error if both are enabled.
> > 
> > In reality (and Alex, please correct me if I'm wrong), the emulated
> > SMC will never generate an INT#6, unlike the real hardware chip. The
> > emulated SMC is just there to say "Yeah, boss, sure, let me get right
> > on that for you!" to OS X, to calm it down and make it think everything
> > is right with its little universe :) The real chip might trigger an
> > interrupt if something's getting too hot, or a fan stopped spinning
> > when it shouldn't have, but that's never going to happen on a VM guest.
> 
> Its main purpose is to signal you dropping your notebook, so the system can 
> shut down your hard drive.
> 
> The main issue I can see with the irq line is that we now potentially have 
> two edge triggered irq sources on a single line, so an OS may get confused.
> 
> But I agree, let's get that one solved later.
> 
> > 
> > OS X doesn't even assume the presence of an FDC, and any guest OS
> > which expects an FDC will never get unexpected conflicting interrupts
> > from the emulated SMC, should the latter be enabled, accidentally or
> > not. So in practice the risk for any trouble should be about zero...
> 
> It may assign the irq line to the applesmc driver, killing the fdc's 
> functionality.
> 
> Speaking of which, does the q35 even have an fdc?
> 
> 
> Alex

I don't think it does but this device seems to be supported with piix as well -
or is this by mistake?

> > 
> > Thanks for helping me think this stuff through !
> > --Gabriel