Re: [Xen-devel] [PATCH 06/14 v4] xen/arm: vpl011: Add a new domctl API to initialize vpl011

[Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>]

Hi Julien,

I was mistaken in my earlier mail about vpl011 init working if it is
moved to libxl__arch_domain_create(). It is failing because as you
have mentioned vuart_pfn is allocated later in xc_dom_build_image().

Can we delay mapping of this page in Xen until the ring buffer is
actually required by the emulation code for reading/writing data. By
that time, the page would have been physically mapped.

Regards,
Bhupinder

On 15 June 2017 at 12:03, Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx> wrote:
> Hi Julien,
>
>
>>>>> diff --git a/tools/libxl/libxl_arch.h b/tools/libxl/libxl_arch.h
>>>>> index 5e1fc60..d1ca9c6 100644
>>>>> --- a/tools/libxl/libxl_arch.h
>>>>> +++ b/tools/libxl/libxl_arch.h
>>>>> @@ -32,6 +32,13 @@ _hidden
>>>>>   int libxl__arch_domain_create(libxl__gc *gc, libxl_domain_config
>>>>> *d_config,
>>>>>                  uint32_t domid);
>>>>>
>>>>> +/* arch specific internal domain creation finish function */
>>>>> +_hidden
>>>>> +int libxl__arch_domain_create_finish(libxl__gc *gc,
>>>>> +                                     libxl_domain_build_info *info,
>>>>> +                                     uint32_t domid,
>>>>> +                                     libxl__domain_build_state *state);
>>>>
>>>>
>>>>
>>>> Can you explain why you need a new arch helper rather than using the
>>>> current
>>>> one?
>>>
>>>
>>> libxl__arch_domain_create() is called from libxl__build_pre(). This
>>> function is called before libxl__build_pv(). By this time the domain
>>> has not be created and I found that if I tried to initialize vpl011
>>> from inside libxl__arch_domain_create() then initialization was
>>> failing due to prepare_ring_for_helper() failing.
>>
>>
>> What do you mean by the domain has not been created? The domain has already
>> been created (you have a domid in hand) when you libxl__build_pre. So the
>> problem is different.
>>
>> Looking at the code, I guess the problem is because the vuart pfn will be
>> allocated by xc_dom_build_image called by libxl_build_pv ->
>> libxl__build_dom.
>>
>>>
>>> So I had to create another function which will be called from
>>> libxl__build_post() after domain has been setup.
>>
>>
>> It looks a bit odd to me to create the vpl011 UART that late in the process
>> because when you read the code you would expect all the hardware to be setup
>> after libxl__arch_domain_finalise_hw_descriptions is called.
>>
>> But I understand it is not possible to do it as the ring has not yet been
>> allocated. So is there a way to allocate the ring before?
>  >
>> Wei, Ian, do you have any opinions on what should the workflow in libxl?
>
> Actually, I had introduced an API xc_get_vuart_gfn() to get the pfn.
> Since it is a fixed pfn, the API can
> return it even before xc_build_dom_image() is called. I tried after
> moving the vpl011_init function to libxl__arch_domain_create() and it
> is working.
>
> Regards,
> Bhupinder

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