[PATCH 3/3] firmware: arm_ffa: Add support for handling notification pending interrupt(NPI)

[Sudeep Holla]

On Wed, Apr 10, 2024 at 12:39:48PM +0100, Sudeep Holla wrote:
> The FF-A uses the notification pending interrupt to inform the receiver
> that it has a pending notification. This is a virtual interrupt and is
> used by the following type of receivers:
>  1. A guest/VM running under a hypervisor.
>  2. An S-EL1 SP running under a S-EL2 SPMC.
> 
> The rules that govern the properties of the NPI are the same as the
> rules for the SRI with couple of exceptions. If the SRI is not supported,
> then an attempt to discover NPI will be made in the driver.
> 
> The handling of NPI is also same as the handling of notification for the
> self/primary VM with ID 0 except the absence of global notification.
>

OK I think I rushed to send this. Bertrand had now convinced me with a
use case that needs the support for both SRI and NPI in the driver.
XEN hypervisor can inject both SRI and NPI to the Dom0. The choice of
NPI over SRI is to avoid the context switch latency with the
FFA_NOTIFICATION_INFO_GET as NPI will just need FFA_NOTIFICATION_GET
which may completely avoid switching to secure side as XEN hyp handles
the same.

--
Regards,
Sudeep