On 5 December 2022 15:59:44 GMT, Icenowy Zheng <uwu@xxxxxxxxxx> wrote: >在 2022-12-05星期一的 15:05 +0000，Conor Dooley写道： >> On Mon, Dec 05, 2022 at 07:03:17PM +0800, Icenowy Zheng wrote: >> > 在 2022-12-05星期一的 10:36 +0000，Conor Dooley写道： >> >> > > You lot all know the situation here a lot more than I do... >> > > I don't think "letting" people use the bare "thead,c900-foo" >> > > makes >> > > much >> > > sense as it gives us no chance to deal with quirks down the line. >> > >> > Well, after rechecking the manual, I found it possible to handle >> > quirks >> > -- T-Head has a custom "mcpuid" CSR (@ RISC-V CSR 0xFC0), which can >> > be >> > used to retrieve some identification info of the core, including >> > its >> > model ID, version, etc; and the T-Head PLIC/CLINT are part of their >> > C906 SoC design that there's another "mapbaddr" CSR that could be >> > used >> > to retrieve the base address of them. >> > >> > So I think it okay to just use "thead,c900-clint" here, and when >> > necessary, try to retrieve mcpuid for dealing with quirks. >> >> I'm not super sure I follow. What's the relevance of "mapbaddr" here? >> We've got a reg property, so I don't think we need "mapbaddr"? > >Yes, it's not relevant to us here, it's only to prove that PLIC/CLINT >is part of C906 "Core Complex". > >> >> For "mcpuid", can you be sure that implementers will not omit setting >> that value to something unique? I'd be happier if we were overly >> clear >> now rather than have some headaches later. Have I missed something? > >These values are set by T-Head instead of individual SoC implementers >as a CPU CSR, and it's not for uniqueness, but it's for identification >of the CPU core revision (thus the PLIC/CLINT that come with it). I really am missing something here that must be obvious to you. Let me try and explain where my gap in understanding is. If someone takes the open cores & makes a minor tweak in the plic how does knowing mcpuid help us identify that that plic is marginally different? I must have missed something that should be apparent and look like an eejit right now! > >> >> > > I don't think that using "thead,openc906-clint", "thead,c900- >> > > clint" >> > > makes all that much sense either, in case someone does something >> > > wacky >> > > with the open-source version of the core. >> > > >> > > That leaves us with either: >> > > "vendor,soc-clint", "thead,openc906-clint", "thead,c900-clint" >> > > or: >> > > "vendor,soc-clint", "thead,c900-clint" >> > > right? >> > > >> > > The first one seems like possibly the better option as you'd >> > > kinda >> > > expect that, in a perfect word, all of the open-source IP >> > > implementations would share quirks etc? >> >
