Re: [Xen-devel] [PATCH 4/7] arm: smccc: handle SMCs according to SMCCC

[Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>]

Hi Julien,

On 09.08.17 13:10, Julien Grall wrote:
> Hi Volodymyr,
>
> CC "THE REST" maintainers to get an opinion on the public headers.
>
> On 08/08/17 21:08, Volodymyr Babchuk wrote:
> > SMCCC (SMC Call Convention) describes how to handle both HVCs and SMCs.
> > SMCCC states that both HVC and SMC are valid conduits to call to a 
> > different
> > firmware functions. Thus, for example PSCI calls can be made both by
> > SMC or HVC. Also SMCCC defines function number coding for such calls.
> > Besides functional calls there are query calls, which allows underling
> > OS determine version, UID and number of functions provided by service
> > provider.
> >
> > This patch adds new file `vsmc.c`, which handles both generic SMCs
> > and HVC according to SMC. At this moment it implements only one
> > service: Standard Hypervisor Service.
> >
> > Standard Hypervisor Service only supports query calls, so caller can
> > ask about hypervisor UID and determine that it is XEN running.
> >
> > This change allows more generic handling for SMCs and HVCs and it can
> > be easily extended to support new services and functions.
> >
> > But, before SMC is forwarded to standard SMCCC handler, it can be routed
> > to a domain monitor, if one is installed.
> >
> > Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> > Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > ---
> >  - Updated description to indicate that this patch affects only SMC 
> > call path.
> >  - added "xen_" prefix to definitions in include/public/arch-arm/smc.h
> >  - moved do_trap_smc() into vsmc.c from traps.c
> >  - replaced all tabs with spaces
> I would have really appreciated a summary of the discussion we had on 
> the previous version regarding the bindings. This is a real blocker for 
> this series and should not be ignored.
While I agree that question about bindings is important, I can't see how 
it affects this patch series. This patch series does not break anything.
Because

1. This series add only new feature: generic hypervisor service with no 
immediate use. All ARM guests are already aware that they are running on 
XEN. All ARM guests know that they call *only* PSCI.
2. I see importance of this patch series for embedded platforms, where 
developer exactly knows what software of which version he/she will run. 
I doubt that server platforms will need something beyond PSCI, which I 
preserved as is.
A I'm not denying importance of SMC bindings, but I think it is not 
blocker for my patches. We can add bindings later, when there will be 
consensus on how they should look. In meantime SMC handler can be used 
by anyone who knows that is available.
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