Hi Drew, On 8/9/26 1:09 AM, Drew Fustini wrote: > On Tue, Jul 14, 2026 at 09:06:55PM +0800, Zhanpeng Zhang wrote: >> The RISC-V IOMMU QoS extension provides iommu_qosid as a per-IOMMU >> global default tag. It is used for IOMMU-originated DDT, CQ, FQ, PQ, and >> MSI accesses, and for device-originated requests when DDTP is in BARE >> mode. >> >> Initialize iommu_qosid to RCID 0 and MCID 0 when the hardware advertises >> QOSID support. Preserve reserved and WPRI bits with read-modify-write, >> and use register readback to reject values which the WARL fields do not >> retain. >> >> Add a qosid attribute to the RISC-V IOMMU class device. Reading returns >> the current RCID and MCID values. Writing the documented >> 'rcid=<rcid> mcid=<mcid>' form updates both fields while preserving the >> other register bits. >> >> Keep this interface separate from resctrl group QoS. The sysfs attribute >> controls the IOMMU-wide default, while resctrl device assignment programs >> per-device DC.ta in translated modes. >> >> Signed-off-by: Zhanpeng Zhang <[email protected]> >> --- >> .../ABI/testing/sysfs-class-iommu-riscv-iommu | 27 +++ >> MAINTAINERS | 10 ++ >> drivers/iommu/riscv/iommu.c | 159 +++++++++++++++++- >> drivers/iommu/riscv/iommu.h | 9 +- >> 4 files changed, 202 insertions(+), 3 deletions(-) >> create mode 100644 Documentation/ABI/testing/sysfs-class-iommu-riscv-iommu >> >> diff --git a/Documentation/ABI/testing/sysfs-class-iommu-riscv-iommu >> b/Documentation/ABI/testing/sysfs-class-iommu-riscv-iommu >> new file mode 100644 >> index 000000000000..b0cd68997f17 >> --- /dev/null >> +++ b/Documentation/ABI/testing/sysfs-class-iommu-riscv-iommu >> @@ -0,0 +1,27 @@ >> +What: /sys/class/iommu/<iommu>/qosid >> +Date: June 2026 >> +KernelVersion: 6.18 >> +Contact: Zhanpeng Zhang <[email protected]> >> +Description: >> + The RISC-V IOMMU global default QoS IDs for this IOMMU. >> + The file is present only when the IOMMU reports the QOSID >> + capability. >> + >> + Reading the file returns the RCID and MCID fields from the >> + iommu_qosid register: >> + >> + rcid=<rcid> mcid=<mcid> >> + >> + Writing the file updates the RCID and MCID fields while >> + preserving reserved/WPRI bits: >> + >> + rcid=<rcid> mcid=<mcid> > > I think it might fit sysfs better if the rcid and mcid are separate > files in that directory. Is there a reason you combine them into one > file? > > Thanks, > Drew
Agreed. There is actually no particular need to update the two fields together; combining them was mostly a habit on my part... I will split the interface into qosid/rcid and qosid/mcid in v2. Thanks, Zhanpeng
