Re: [RFC v1 0/5] Introduce SCI-mediator feature

[Oleksii Moisieiev <Oleksii_Moisieiev@xxxxxxxx>]

Hi Oleksandr,

On Thu, Dec 16, 2021 at 02:33:28AM +0200, Oleksandr wrote:
> 
> On 14.12.21 11:34, Oleksii Moisieiev wrote:
> 
> 
> Hi Oleksii
> 
> > Introducing the feature, called SCI mediator.
> > It's purpose is to redirect SCMI requests from the domains to firmware
> > (SCP, ATF etc), which controls the power/clock/resets etc.
> > The idea is to make SCP firmware (or similar, such as AT-F) responsible for
> > control power/clock/resets and provide SCMI interface so controls can be 
> > shared
> > between the Domains.
> > Originally, we've met a problem, that the devices, shared between different
> > Domains, can't have an access to HW registers to work with 
> > clocks/resets/power
> > etc. You have to pass cpg to the Domain, so the devices can access HW 
> > directly.
> > The solution for this is to move HW controls over power/clock/resets to
> > SCP firmware and use Linux-kernel SCMI drivers to pass requests to SCP.
> > Xen is responsible for permissions setting, so Domain can access only to
> > power/clock/resets which are related to this Domain. Also XEN is the 
> > mediator
> > which redirects SCMI requests, adding agentID so firmware should know the
> > sender.
> > SMC is currently used as transport, but this should be configurable.
> > 
> > Here is the high level design:
> > 
> > SCI (System Control Interface) feature can be enabled in xen_config:
> > > CONFIG_SCI=y
> > Mediator can be configured:
> > > CONFIG_SCMI_SMC=y
> > Currently, only SCMI_SMC mediator is implemented, which using shared memory
> > region to communicate with firmware and SMC as transport.
> > 
> > Xen scmi should be configured in the device-tree.
> > Format is the following:
> >     cpu_scp_shm: scp-shmem@0x53FF0000 {
> >             compatible = "arm,scmi-shmem";
> >             reg = <0x0 0x53FF0000 0x0 0x1000>;
> >     };
> > 
> >     firmware {
> >             scmi {
> >                     compatible = "arm,scmi-smc";
> >                     arm,smc-id = <0x82000002>;
> >                     shmem = <&cpu_scp_shm>;
> >                     #address-cells = <1>;
> >                     #size-cells = <0>;
> > 
> >                     scmi_power: protocol@11 {
> >                             reg = <0x11>;
> >                             #power-domain-cells = <1>;
> >                     };
> > 
> >                     scmi_clock: protocol@14 {
> >                             reg = <0x14>;
> >                             #clock-cells = <1>;
> >                     };
> > 
> >                     scmi_reset: protocol@16 {
> >                             reg = <0x16>;
> >                             #reset-cells = <1>;
> >                     };
> >             };
> >     };
> > 
> > Where:
> > &cpu_scp_shm is the shared memory for scmi buffers;
> > 0x53FF0000, size 0x1000 is the platform specific free address, which provide
> > space for the communication.
> > &scmi node, which should be copied to Dom0 device-tree.
> > 
> > Device configured to use scmi:
> > &avb {
> >     scmi_devid = <0>;
> >     clocks = <&scmi_clock 0>;
> >     power-domains = <&scmi_power 0>;
> >     resets = <&scmi_reset 0>;
> > };
> > 
> > Where:
> > scmi_devid - id from the firmware, which is assigned for AVB.
> > 
> > During initialization, XEN scans probes the first SCI-mediator driver which 
> > has
> > matching node in the device-tree. If no device-tree was provided, then the
> > first registered mediator driver should be probed.
> > 
> > DomX should be configured:
> > Device-tree should include the same nodes, described above.
> > &cpu_scp_shm should be altered during domain creation. Xen allocates free 
> > page
> > from the memory region, provided in &cpu_scp_shm in XEN device-tree, so each
> > domain should have unique page. Nodes &cpu_scp_shm and /firmware/scmi 
> > should be
> > copied from partial device-tree to domain device-tree, so kernel can 
> > initialize
> > scmi driver.
> > 
> > SCI mediator can be enabled in dom.cfg the following way:
> > > sci = "scmi_smc"
> > which sets scmi_smc to be used for the domain.
> 
> 
> Great work! I can imagine this is going to be nice feature once upstreamed.
> 
> I am wondering, would the Xen (with the required updates of course) also be
> able to send it's own requests to the SCP? For example, to control overall
> system performance (CPU frequency)
> 
> or other let's say important power management task.
> 

I think yes. In current implementation Xen register itself as
privilleged agent and use it's own channel to request 
which is used to get agent configuration and process device permissions.
I think this channel can also be used to do some configuration tasks
via SCMI. But this will require updates.

--
Oleksii.
> 
> > 
> > Oleksii Moisieiev (5):
> >    xen/arm: add support for Renesas R-Car Gen3 platform
> >    xen/arm: add generic SCI mediator framework
> >    xen/arm: introduce SCMI-SMC mediator driver
> >    tools/arm: add "scmi_smc" option to xl.cfg
> >    xen/arm: add SCI mediator support for DomUs
> > 
> >   MAINTAINERS                       |   6 +
> >   docs/man/xl.cfg.5.pod.in          |  22 +
> >   tools/include/libxl.h             |   5 +
> >   tools/include/xenctrl.h           |   3 +
> >   tools/include/xenguest.h          |   2 +
> >   tools/libs/ctrl/xc_domain.c       |  23 +
> >   tools/libs/guest/xg_dom_arm.c     |   5 +-
> >   tools/libs/light/libxl_arm.c      | 122 ++++-
> >   tools/libs/light/libxl_create.c   |  54 +-
> >   tools/libs/light/libxl_dom.c      |   1 +
> >   tools/libs/light/libxl_internal.h |   4 +
> >   tools/libs/light/libxl_types.idl  |   6 +
> >   tools/xl/xl_parse.c               |   9 +
> >   xen/arch/arm/Kconfig              |  10 +
> >   xen/arch/arm/Makefile             |   1 +
> >   xen/arch/arm/domain.c             |  24 +
> >   xen/arch/arm/domain_build.c       |  11 +
> >   xen/arch/arm/domctl.c             |  15 +
> >   xen/arch/arm/platforms/Makefile   |   1 +
> >   xen/arch/arm/platforms/rcar3.c    |  47 ++
> >   xen/arch/arm/sci/Kconfig          |  10 +
> >   xen/arch/arm/sci/Makefile         |   2 +
> >   xen/arch/arm/sci/sci.c            | 128 +++++
> >   xen/arch/arm/sci/scmi_smc.c       | 795 ++++++++++++++++++++++++++++++
> >   xen/arch/arm/setup.c              |   1 +
> >   xen/arch/arm/xen.lds.S            |   7 +
> >   xen/include/asm-arm/domain.h      |   4 +
> >   xen/include/asm-arm/sci/sci.h     | 162 ++++++
> >   xen/include/public/arch-arm.h     |  11 +
> >   xen/include/public/domctl.h       |   9 +
> >   30 files changed, 1485 insertions(+), 15 deletions(-)
> >   create mode 100644 xen/arch/arm/platforms/rcar3.c
> >   create mode 100644 xen/arch/arm/sci/Kconfig
> >   create mode 100644 xen/arch/arm/sci/Makefile
> >   create mode 100644 xen/arch/arm/sci/sci.c
> >   create mode 100644 xen/arch/arm/sci/scmi_smc.c
> >   create mode 100644 xen/include/asm-arm/sci/sci.h
> > 
> -- 
> Regards,
> 
> Oleksandr Tyshchenko
>