Re: [RFC PATCH v5 03/10] xen/arm: scmi-smc: passthrough SCMI SMC to domain, single agent

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 22 Jul 2025, Oleksii Moisieiev wrote:
> From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
> 
> The commit 3e322bef8bc0 ("xen/arm: firmware: Add SCMI over SMC calls
> handling layer") introduces simple driver which forwards SCMI over SMC
> calls from hwdom/dom0 to EL3 firmware (TF-A) with a single SCMI OSPM agent
> support. While it is working gracefully for hwdom/dom0 use case it doesn't
> cover "thin Dom0 with guest domain, which serves as Driver domain"
> use-case. In this case HW need to be enable in Driver domain and dom0 is
> performing only control functions.
> 
> The EL3 SCMI firmware (TF-A) with a single SCMI OSPM agent support is
> pretty generic case for the default vendors SDK and new platforms.
> 
> This patch enables passthrough of SCMI SMC single agent interface to the
> one guest domain serving as Driver domain.
> 
> Configure Dom0 to enable SCMI passthrough:
> 
>  - dom0: add scmi_smc_passthrough to the Xen Command Line
> 
> Enabled SCMI passthrough for guest using toolstack in the following way:
> 
>  - domD: xl.cfg add "arm_sci" option as below
> 
>    arm_sci = "type=scmi_smc"
> 
>  - domD: xl.cfg enable access to the "arm,scmi-shmem"
> 
> iomem = [
>     "47ff0,1@22001",
> ]
> 
>  - domD: add SCMI nodes to the Driver domain partial device tree as in the
>  below example:
> 
> passthrough {
>    scmi_shm_0: sram@22001000 {
>        compatible = "arm,scmi-shmem";
>        reg = <0x0 0x22001000 0x0 0x1000>;
>    };
> 
>    firmware {
>         compatible = "simple-bus";
>             scmi: scmi {
>                 compatible = "arm,scmi-smc";
>                 shmem = <&scmi_shm_0>;
>                 ...
>             }
>     }
> }
> 
> dom0less case configuration:
> 
> - add "xen,sci_type" property for required DomU ("xen,domain") node
> 
>    xen,sci_type="scmi_smc"
> 
> - add scmi nodes to the Driver domain partial device tree the same way
> as above and enable access to the "arm,scmi-shmem" according to
> dom0less documentation. For example:
> 
>   scmi_shm_0: sram@22001000 {
>         compatible = "arm,scmi-shmem";
>         reg = <0x00 0x22001000 0x00 0x1000>;
> ->        xen,reg = <0x0 0x47ff0000 0x0 0x1000 0x0 0x22001000>;
> ->        xen,force-assign-without-iommu;
>   };
> 
> The SCMI SMC single agent interface can be enabled for one and only one
> domain. In general, the configuration is similar to any other HW
> passthrough, except explicitly enabling SCMI with "arm_sci" xl.cfg option.
> 
> Note that "arm,scmi-smc" and "arm,scmi-shmem" nodes will be removed from
> dom0/hwdom DT in case of

This patch needs to be rebased, other than that, it is OK