Re: [Qemu-devel] RFC: ehci -> uhci handoff suggestions

[Gerd Hoffmann]

On 05/25/10 15:40, David S. Ahern wrote:
> USB 2.0 leverages companion UHCI or OHCI host controllers for full and
> low speed devices. I do not see an appropriate means for doing that bus
> transition and could use some suggestions.

Hmm.  Well.  That doesn't really fit into the qdev tree model ...

> As I understand the code at this point it is a top down setup: device
> added, bus found, device attached.

Devices are always added to some bus.  In the case of usb the devices 
can also be attached/detached.  Emulated devices usually attached right 
after creating them.  Host devices are attached when a matching physical 
device shows up.

> ie., key point is the expectation that the bus to which the device is
> assigned is known early in the code path.

Yes.  You can even specify the bus you want attach the device to.

>      --------------------      --------------------
>     |   EHCI controller  |--->|    UHCI / OHCI     |
>      --------------------      --------------------
>               |                         |
>      --------------------      --------------------
>     |  USB device model  |    |  USB device model  |
>     |    (or driver )    |    |    (or driver )    |
>      --------------------      --------------------
>           high speed             full / low speed
>
>
> To know which bus to attach it to the device needs to be queried/probed
> for basic information - something the current architecture does not have.

USB devices can support both 1.1 and 2.0, right?  Who decides which 
protocol is used then?  I think the OS can speak 1.1 to the device even 
in case a ehci controller is present (but unused by the OS), right?

> Suggestions?

Maybe it makes more sense to look at ehci/uhci as *one* (physical) 
device with multiple interfaces?  They share the physical ports after 
all, at least on real hardware.

The tricky case is assigning host devices, right?  For the emulated ones 
we can probably could get away by simply forcing them into 2.0-only or 
1.1-only mode depending on which bus they got attached to.

cheers,
  Gerd