Re: [Qemu-devel] [PATCH V14 2/7] Add TPM (frontend) hardware interface (TPM TIS) to Qemu

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Feb 21, 2012 at 10:05:26AM -0500, Stefan Berger wrote:
> On 02/21/2012 07:18 AM, Michael S. Tsirkin wrote:
> >On Tue, Feb 21, 2012 at 06:19:26AM -0500, Stefan Berger wrote:
> >>On 02/20/2012 10:18 PM, Michael S. Tsirkin wrote:
> >>>On Mon, Feb 20, 2012 at 07:43:05PM -0500, Stefan Berger wrote:
> >>>>On 02/20/2012 05:02 PM, Michael S. Tsirkin wrote:
> >>>>>On Wed, Dec 14, 2011 at 08:43:17AM -0500, Stefan Berger wrote:
> >>>Alternatively, I imagined that you can pass a copy
> >>>or pointer of the necessary state to the backend,
> >>>which queues the command and wakes the worker.
> >>>In the reverse direction, backend queues a response
> >>>and when OS polls you dequeue it and update state.
> >>>
> >>The OS doesn't necessarily need to poll. It is just one mode of
> >>operation of the OS, the other being interrupt-driven where the
> >>backend raises the interrupt once it has delivered the response to
> >>the frontend.
> >>
> >>
> >>    Stefan
> >So you will also need to signal the frontend when it
> >must interrupt the guest. This is not a problem,
> >for example you can use a qemu_eventfd object for this.
> >
> 
> When the backend delivers the response it checks whether the
> interface is used in interrupt mode and raises the interrupt.

IMO it's the frontend that should send interrupts.
Yes it kind of works for isa anyway, but e.g. pci
needs to update configuration etc.

> The
> backend enters the frontend code with a callback. In this function
> also a signal is sent that may wake up the main thread that, upon
> suspend, may be waiting for the last command to be processed and be
> sleeping on a condition variable.
> 
> I now added a function to the backend interface that is invoked by
> the frontend to notify the backend of a TPM request. The backend
> code can then either notify a thread (passthrough and libtpms
> driver) or create a response right away and invoke that callback to
> the front-end to deliver the response (null driver). How frontend
> and backend handle notifications is isolated to the frontend and
> backend with some backends (libtpms, passthough) sharing the code
> for how the notification is done.
> 
> Stefan

Right. And all the locking/threading can then be internal to the backend.

-- 
MST