search

riscv-non-isa / riscv-iommu

RISC-V IOMMU Specification
https://jira.riscv.org/browse/RVG-55
Creative Commons Attribution 4.0 International
98 stars 17 forks source link

Sorry,how to configure the value of capabilities.PAS? #284

Closed augsug closed 8 months ago

augsug commented 8 months ago

PAS is a 6-bits field in capabilities,which means Physical Address Size supported by the IOMMU.But how can i configure this filed?

WXWorkLocal_20240313101734

ved-rivos commented 8 months ago

The capabilities register is used to report the capabilities of the IOMMU hardware. This is a read-only register used for enumeration and is not a configuration register. So the PAS (and other hardware capabilities) are not software configurable. Some hardware implementations, such as soft-IPs, may have build time configurations for the hardware and may also support mechanisms like straps/fuses to configure the hardware at implementation time.

ved-rivos commented 8 months ago

I hope that addressed the question. Please feel free to ask if there are further questions.

augsug commented 8 months ago

I got u. if i set this field in 6'b0000_01，what does this mean?Physical Address Size is 4KiB or something ? look forward to your advice:)

ved-rivos commented 8 months ago

@augsug - a value of 6'b0000_01 implies 1-bit and a value of 6'b1110_00 implies 56-bit.