[RFC PATCH 4/7] iommu/riscv: Program QoS IDs for assigned groups

[Drew Fustini]

On Tue, Jul 14, 2026 at 09:06:54PM +0800, Zhanpeng Zhang wrote:
> Program RCID and MCID for RISC-V IOMMU groups through the device context
> TA fields. The resctrl group assignment is per device group, so reject
> BARE mode where only the per-IOMMU iommu_qosid global default is
> available.
> 
> Validate every group member, firmware ID, device context, field value,
> and QoS ID capability before changing hardware. Then update all members
> through the checked IOMMU group helper so a validation failure leaves the
> group unchanged.
> 
> Serialize DC.ta changes with context setup under qosid_lock. Change only
> the RCID and MCID fields with ordinary accesses so fixed DDT mappings are
> not subject to atomic LR/SC operations, invalidate active device contexts
> after an update, and clear the IDs when a device is released.
> 
> Signed-off-by: Zhanpeng Zhang <zhangzhanpeng.jasper at bytedance.com>
> ---
>  arch/riscv/include/asm/qos.h     |  16 +++
>  drivers/iommu/riscv/iommu-bits.h |  15 +++
>  drivers/iommu/riscv/iommu.c      | 200 ++++++++++++++++++++++++++++++-
>  drivers/iommu/riscv/iommu.h      |   3 +
>  4 files changed, 232 insertions(+), 2 deletions(-)
> 
[..]
> +static void riscv_iommu_dc_update_qosid(struct riscv_iommu_device *iommu,
> +					struct riscv_iommu_dc *dc,
> +					u32 rcid, u32 mcid)
> +{
> +	u64 qos_ta = riscv_iommu_qosid_ta(rcid, mcid);
> +	u64 ta;
> +
> +	lockdep_assert_held(&iommu->qosid_lock);

It seems that qosid_lock is not defined until the next patch. I think
you should move the definition to this patch so that the series is
bisectable.

Thanks,
Drew