Re: [PATCH 08/17 v5] xen/arm: vpl011: Add a new domctl API to initialize vpl011

[Julien Grall <julien.grall@arm.com>]

On 23/06/17 14:17, Julien Grall wrote:
>
>
> On 23/06/17 00:04, Stefano Stabellini wrote:
>>> diff --git a/tools/libxc/include/xenctrl.h
>>> b/tools/libxc/include/xenctrl.h
>>> index 1629f41..26f3d1e 100644
>>> --- a/tools/libxc/include/xenctrl.h
>>> +++ b/tools/libxc/include/xenctrl.h
>>> @@ -885,6 +885,26 @@ int xc_vcpu_getcontext(xc_interface *xch,
>>>                         uint32_t vcpu,
>>>                         vcpu_guest_context_any_t *ctxt);
>>>
>>> +#if defined (__arm__) || defined(__aarch64__)
>>> +/**
>>> + * This function initializes the vpl011 emulation and returns
>>> + * the event to be used by the backend for communicating with
>>> + * the emulation code.
>>> + *
>>> + * @parm xch a handle to an open hypervisor interface
>>> + * @parm domid the domain to get information from
>>> + * @parm console_domid the domid of the backend console
>>> + * @parm gfn the guest pfn to be used as the ring buffer
>>> + * @parm evtchn the event channel to be used for events
>>> + * @return 0 on success, negative error on failure
>>> + */
>>> +int xc_dom_vpl011_init(xc_interface *xch,
>>> +                       uint32_t domid,
>>> +                       uint32_t console_domid,
>>> +                       xen_pfn_t gfn,
>>> +                       evtchn_port_t *evtchn);
>>> +#endif
>>
>> Actually, the pattern is to define the xc_ function on all architecture
>> but only return ENOSYS where it's not implemented, see
>> xc_vcpu_get_extstate.
>
> Well, I think the main reason behind if to avoid dummy call to the
> hypervisor. But effectively the hypervisor will return a proper error.

Actually, looking at the public header. This is because 
vcpu_get_extstate structure is only available on x86. Whereas 
vpl011_init is available for all the architecture even though only ARM 
effectively implementing it.

But my point stands below, there is no harm to implement it for x86 as 
it would compile on any platform.

>
> As the call is not made in common code, I would make this function
> compile on all the platform (there are nothing arch specific in it).

Cheers,

-- 
Julien Grall

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