Re: [Xen-devel] [PATCH v3] xen/arm: enable clocks used by the hypervisor

[Julien Grall <julien.grall@xxxxxxx>]

On 08/07/16 11:40, Dirk Behme wrote:
> Hi Michael and Julien,
>
> On 08.07.2016 11:34, Julien Grall wrote:
> > Hi Dirk,
> >
> > On 08/07/16 08:44, Dirk Behme wrote:
> > > Xen hypervisor drivers might replace native OS drivers. The result is
> > > that some important clocks that are enabled by the OS in the non-Xen
> > > case are not properly enabled in the presence of Xen. The clocks
> > > property enumerates the clocks that must be enabled by the Xen clock
> > > consumer.
> > >
> > > An example is a serial driver enabled by the hypervisor. Xen must
> > I would say "An example is the UART used by the hypervisor."
> >
> > > consume and enable these clocks in the OS to ensure behavior continues
> > > after firmware configures the UART hardware and corresponding clock
> > > harder.
> > What do you mean by "harder"?
> >
> > Also, relying on DOM0 to enable the clock looks very wrong to me and you
> > give an example which prove that. The UART will be used before hand by
> > Xen, however it will not be possible to use it if you expect DOM0 to
> > enable the clock (or even modify the clock frequency).
> >
> > The clock should be enabled either by the firmware or Xen. But not DOM0.
> > DOM0 should not touch this clock at all.
> >
> > Furthermore, this property could be used for clock associated to device
> > that will be passthrough-ed to a guest. In this case, the clock would be
> > enabled even if the device is not in use which will result more power
> > consumption.
>
> I took the description directly from Michael's proposal
>
> http://www.spinics.net/lists/arm-kernel/msg516576.html
>
> Would it be possible that you two experts agree on the exact wording you
> like to see?
I think the wording suggested by Mark in [1] represents better what we 
would like to achieve with this property.
Regards,

[1] https://www.spinics.net/lists/arm-kernel/msg516158.html

--
Julien Grall

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