On Fri, Sep 16, 2011 at 09:17:54PM -0500, Anthony Liguori wrote: > On 09/16/2011 07:48 PM, Edgar E. Iglesias wrote: > >On Fri, Sep 16, 2011 at 07:47:57PM +0300, Gleb Natapov wrote: > >>On Thu, Sep 15, 2011 at 03:50:28PM -0500, Anthony Liguori wrote: > >>>On 09/15/2011 03:29 PM, Gleb Natapov wrote: > >>>>On Thu, Sep 15, 2011 at 12:51:23PM -0500, Anthony Liguori wrote: > >>>>>On 09/15/2011 11:59 AM, Gleb Natapov wrote: > >>>>>>On Thu, Sep 15, 2011 at 11:33:00AM -0500, Anthony Liguori wrote: > >>>>>>>On 09/15/2011 10:38 AM, Gleb Natapov wrote: > >>>>>>>>On Thu, Sep 15, 2011 at 10:28:52AM -0500, Anthony Liguori wrote: > >>>>>>>>>On 09/15/2011 09:25 AM, Gleb Natapov wrote: > >>>>>>>>> > >>>>>>>>>There is no canonical parent link. A device may have multiple (more > >>>>>>>>>or less equivalent) parents. > >>>>>>>>> > >>>>>>>>>What should be treated as the "canonical" link depends on what > >>>>>>>>>you're trying to do. In the case of OF, you want to treat the bus > >>>>>>>>>as a parent. If a device happens to sit on multiple buses, I'm not > >>>>>>>>>really sure what you do. > >>>>>>>>> > >>>>>>>>Yes, "canonical" is a link to a bus. Can you give an example of a > >>>>>>>>device > >>>>>>>>that sits on multiple buses? > >>>>>>> > >>>>>>>Not all devices buses that they sit on. > >>>>>>> > >>>>>>Missing "have"? If device has no bus how do you talk to it? Who carries > >>>>>>the signal from a cpu to a device? > >>>>>> > >>>>>>>A good example is our favorite one to debate--the PIIX3. Devices > >>>>>>PIIX3 is a collection of devices, not a device. > >>>>>> > >>>>>>>like the UART don't sit on a bus. They don't have any links at all. > >>>>>>In PC UART sits on isa bus. How device can have no links at all? It just > >>>>>>glued to a motherboard not touching any wires? > >>>>> > >>>>>A bus implies a bidirectional relationship. IOW, the device has to > >>>>>know that it sits on a ISA bus to be an ISA device. > >>>>> > >>>>And ISA device with UART on it definitely knows that. > > > >IMO, this discussion is going nowhere, Partly because assummptions are > >beeing made about how hardware "works". > > > >Hardware works the way it gets designed, and it can be desinged in pretty > >much anyway you want. > > > >When it comes to devives, you can design them in a way so they become very > >dependent on a specific bus. But you can also design them in a more genric > >way so that they become bus agnostic. Then you just need to connect a bus > >adaptor that hooks things up to the particular bus the device needs to be > >hooked up to. > > > >Sometimes, the bus adaptor becomes more like like wrapper that is part > >of the logic, other times, the bus adaptor is just a passthru unit. > > > >QEMU should allow us to model devices in a a bus agnostic way. > > And this is the problem to fix in qdev. We need to kill buses in > qdev. The approach really boils down to: > > 1) Add unique names to devices (this is needed because buses must > have names because they must be addressable). > > 2) Eliminate any device that has two bus instances in it. I'm > pretty sure IDE is the only example of this. > > 3) Move all BusState functionality to DeviceState and eliminate > buses. This is a compatibility breaker but a critical change. > Anthony Liguori
I agree. Because busses are in the eye of the beholder. For some devices a clock connection is it's main relationship with the system. For others, maybe a "back" channel or link is the only connectino. For the common device maybe the "main" bus on which CPU's is are connected is the master bus. Cheers
