Re: [Xen-devel] ARM Xen Bug #45: Is there a solution?

[Julien Grall <julien.grall@xxxxxxx>]

On 25/05/2016 16:10, Dirk Behme wrote:
> Hi Julien,
Hello Dirk,

> On 24.05.2016 22:05, Julien Grall wrote:
> > On 24/05/2016 14:39, Dirk Behme wrote:
> > > Hi Julien,
> > Hello Dirk,
> >
> > > On 23.05.2016 22:15, Julien Grall wrote:
> > > > Hello Dirk,
> > > >
> > > > > is there a solution for
> > > > >
> > > > > arm: domain 0 disables clocks which are in fact being used
> > > > > http://bugs.xenproject.org/xen/bug/45
> > > > >
> > > > > ?
> > > > >
> > > > > On an ARM based board I have to use 'clk_ignore_unused' preventing
> > > > > that
> > > > > Dom0 disables the UART clock for the console UART configured with
> > > > > console=hvc0.
> > > > There is no better solution than passing "clk_ignore_unused" on the
> > > > kernel command line so far.
> > >
> > > What would be the solution for this issue? The
> > >
> > > "propagate any clock related properties from the UART
> > > node into the Xen hypervisor node"
> > >
> > > mentioned in the ticket?
> > That is correct. Xen would copy the property "clocks" of the UART into
> > the hypervisor node.
> >
> > DOM0 would then parse the clocks associated to this node and mark them
> > as used by Xen (I think CLK_IGNORE_UNUSED could do the job for us).
>
> I've started to look into this:
>
> I'd think in arm_uart.c in dt_uart_init() after
>
> if ( !dev )
>
> we know the UART node we are looking for. From this we have to read the
> clock configuration.
>
> To be clarified: How to read the clock configuration? I couldn't find
> any convenient function dt_device_get_clock() or similar for that.
Xen does not need to parse the content of the property "clocks" but copy 
the raw value to the DOM0 DT.
You cand find the value of a property with dt_get_property.

> Now, we have the clocks we are looking for.
>
> These are needed in domain_build.c in make_hypervisor_node(), then.
>
> To be clarified: How to pass the clock configuration from arm_uart.c to
> domain_build.c (and not break the non-dt / non-ARM platforms)?
>
> Any ideas or comments?
All the devices (UART included) used by Xen will return DOMID_XEN when 
dt_device_used_by is called to the node.
You could use it to collect the clocks of all those devices and gather 
the value in a single property to be created in the hypervisor node.
Regards,

--
Julien Grall

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