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
