Re: [RFC PATCH 6/7] riscv_cbqri: Assign IOMMU groups to resource groups

[Drew Fustini <fustini@kernel.org>]

On Tue, Jul 14, 2026 at 09:06:56PM +0800, Zhanpeng Zhang wrote:
> Allow the resctrl devices file to accept iommu_group:<id> tokens on
> RISC-V and map the target resource group's closid and rmid values to
> RCID and MCID.
> 
> Record non-default assignments in an RCU-protected binding list rather
> than inferring membership from hardware IDs, which may be shared. Keep a
> parent reference obtained by numeric group lookup so the binding does not
> keep an empty group's devices kobject active, and prune bindings after
> their group becomes inactive.
> 
> Publish an explicit UPDATING state while hardware changes. Paging-domain
> attachment rejects that transient state. Static FSC=Bare transitions
> preserve the current IDs so a mandatory release-domain attachment cannot
> fail. After the checked group update succeeds, publish the packed IDs. A
> validation failure restores the previous active state without partially
> changing hardware.
> 
> Moving an IOMMU group to the default resource group resets its hardware
> state and removes the software binding. Device contexts created later for
> an assigned group inherit the IDs through the RCU lookup path.
> 
> Signed-off-by: Zhanpeng Zhang <zhangzhanpeng.jasper@bytedance.com>
[..]
> diff --git a/drivers/resctrl/cbqri_iommu.c b/drivers/resctrl/cbqri_iommu.c
> new file mode 100644
> index 000000000000..4086c32546bd
> --- /dev/null
> +++ b/drivers/resctrl/cbqri_iommu.c
[..]
> +#include <asm/qos.h>
> +
> +#define IOMMU_GROUP_TOKEN	"iommu_group:"

I am wondering if maybe this should be parsed at the resctrl layer since
it could be possible for RISC-V and ARM to both use the iommu_group
token. I am hoping that Reinette and the MPAM developrs will add their
prespectives on the the resctrl devices file and at what level the
tokens should be parsed.

Thanks,
Drew