Re: [edk2-devel] [PATCH 0/4] RISC-V: Add support for Sstc extension
Hi Pedro, On Fri, Jan 05, 2024 at 07:10:40PM +, Pedro Falcato wrote: > On Wed, Jan 3, 2024 at 1:59 PM Sunil V L wrote: > > > > This series adds the support for RISV-V Sstc extension in EDK2 timer > > nit: RISC-V > > implementation. Sstc extension allows S-mode software to program the > > timer directly without using SBI calls. > > > > Currently, PCD variable is used to detect whether feature is enabled. By > > default the feature is enabled and platforms need to set the PCD to > > disable the feature if Sstc is not supported. > > > > For RiscVVirtQemu, it is disabled by default (until extension discovery > > feature is enabled). > > I'm curious, what do you want Sstc for? Is the performance difference > measurable (if so, please post numbers, and add them to the commit)? > Does it have any other advantages? > Good question. Without Sstc, timer needs to be programmed using SBI call. The number of instructions via SBI call is way more than a simple CSR access. So, when the CPU supports Sstc, there is no point in using SBI call. The issue with SBI call will be worse under KVM since it has to emulate the timer. Supporting Sstc is futuristic. The platforms can decide not to implement SBI TIME interface at all since they have Sstc. In that case, EDK2 needs to have option to support either. Thanks, Sunil -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#113353): https://edk2.groups.io/g/devel/message/113353 Mute This Topic: https://groups.io/mt/103501836/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
Re: [edk2-devel] [PATCH 0/4] RISC-V: Add support for Sstc extension
On Wed, Jan 3, 2024 at 1:59 PM Sunil V L wrote: > > This series adds the support for RISV-V Sstc extension in EDK2 timer nit: RISC-V > implementation. Sstc extension allows S-mode software to program the > timer directly without using SBI calls. > > Currently, PCD variable is used to detect whether feature is enabled. By > default the feature is enabled and platforms need to set the PCD to > disable the feature if Sstc is not supported. > > For RiscVVirtQemu, it is disabled by default (until extension discovery > feature is enabled). I'm curious, what do you want Sstc for? Is the performance difference measurable (if so, please post numbers, and add them to the commit)? Does it have any other advantages? -- Pedro -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#113315): https://edk2.groups.io/g/devel/message/113315 Mute This Topic: https://groups.io/mt/103501836/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
[edk2-devel] [PATCH 0/4] RISC-V: Add support for Sstc extension
This series adds the support for RISV-V Sstc extension in EDK2 timer implementation. Sstc extension allows S-mode software to program the timer directly without using SBI calls. Currently, PCD variable is used to detect whether feature is enabled. By default the feature is enabled and platforms need to set the PCD to disable the feature if Sstc is not supported. For RiscVVirtQemu, it is disabled by default (until extension discovery feature is enabled). Cc: Andrei Warkentin Cc: Ard Biesheuvel Cc: Gerd Hoffmann Cc: Jiewen Yao Cc: Laszlo Ersek Cc: Rahul Kumar Cc: Ray Ni Cc: Michael D Kinney Cc: Liming Gao Cc: Zhiguang Liu Sunil V L (4): MdePkg.dec: RISC-V: Define override bit for Sstc extension MdePkg/BaseLib: RISC-V: Add function to update stimecmp register UefiCpuPkg/CpuTimerDxeRiscV64: Add support for Sstc OvmfPkg/RiscVVirt: Override Sstc extension MdePkg/MdePkg.dec | 2 ++ OvmfPkg/RiscVVirt/RiscVVirt.dsc.inc | 2 +- .../CpuTimerDxeRiscV64/CpuTimerDxeRiscV64.inf | 1 + MdePkg/Include/Library/BaseLib.h | 5 .../Include/Register/RiscV64/RiscVEncoding.h | 3 ++ UefiCpuPkg/CpuTimerDxeRiscV64/Timer.h | 2 ++ UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c | 30 +-- MdePkg/Library/BaseLib/RiscV64/ReadTimer.S| 7 + 8 files changed, 49 insertions(+), 3 deletions(-) -- 2.34.1 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#113092): https://edk2.groups.io/g/devel/message/113092 Mute This Topic: https://groups.io/mt/103501836/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
