Re: [PATCH v4] xen/arm: Add a clock property

Julien Grall
2016-07-20T12:10:14Z

On 20/07/16 12:49, Geert Uytterhoeven wrote:
> Hi Julien,
>
> On Wed, Jul 20, 2016 at 1:01 PM, Julien Grall <julien.grall@arm.com> wrote:
>> On 20/07/16 10:43, Geert Uytterhoeven wrote:
>>> On Tue, Jul 12, 2016 at 9:46 AM, Dirk Behme <dirk.behme@de.bosch.com>
>>> wrote:
>>>>
>>>> Clocks described by this property are reserved for use by Xen, and the OS
>>>> must not alter their state any way, such as disabling or gating a clock,
>>>> or modifying its rate. Ensuring this may impose constraints on parent
>>>> clocks or other resources used by the clock tree.
>>>>
>>>> This property is used to proxy clocks for devices Xen has taken ownership
>>>> of, such as UARTs, for which the associated clock controller(s) remain
>>>> under the control of Dom0.
>>>
>>>
>>> I'm not familiar with using XEN at all, but I'm a bit puzzled...
>>>
>>> Can't you just add a clocks property to the (virtual) serial device node
>>> in DT?
>>> Then the (virtual) serial device driver can get and enable the clock?
>>
>> There is no DT node for the Xen console (hvc). The UART used by Xen will be
>> completely removed from the Device tree.
>
> Why is it removed?

Because the device is used exclusively by Xen and DOM0 should not touch
it at all (IRQs and MMIOs are not mapped).

Regards,

--
Julien Grall