Re: ARM Xen Bug #45: Is there a solution?

[Dirk Behme <dirk.behme@gmail.com>]

Hi Julien,

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.

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?


Best regards

Dirk


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