Re: Xen ARM - Exposing a PL011 to the guest

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

Hi,

On 06/01/17 21:54, Stefano Stabellini wrote:
> On Fri, 6 Jan 2017, Bhupinder Thakur wrote:
>> Hi,
>>
>> I am trying to allocate a new SPI VIRQ for sending pl011 interrupt to
>> the guest OS. Currently Xen does not allow to allocate a SPI VIRQ for
>> a guest domain. I tried allocating a new SPI VIRQ by calling
>> vgic_allocate_spi() but it failed as the SPI VIRQ range for the guests
>> is limited to 0 (vgic_num_irqs() return 32 and therefore in effect
>> says that no SPI VIRQ can be allocated because below 32 are for
>> PPI/SGI VIRQs).
>
> Yes, you should use vgic_allocate_virq. For that to work, you need to
> make sure that nr_spis for the domain is > 0. Given that nr_spis is
> passed from libxl by calling xc_domain_create, I would set nr_spis to 1
> in libxl__arch_domain_prepare_config.

Before I forgot, this would need to be documented to allow people to 
easily use interrupt routing (for device passthrough) when PL011 enabled.

I would suggest to define the SPI used by the PL011 in 
include/public/arch-arm.h and the number of SPIs reserved 
(GUEST_NR_RESERVED_SPIS). This would avoid an hardcoded number in the 
code and easily extension whether we need more SPIs later on (I have the 
host bridge emulation in mind).

Cheers,

-- 
Julien Grall

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