On 6 December 2022 03:46:11 GMT, Icenowy Zheng <uwu@xxxxxxxxxx> wrote: >在 2022-12-05星期一的 16:54 +0000，Conor Dooley写道： >> >> >> 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? > >No, but my point is that in this situation we shouldn't use C900 >compatible at all because it's no longer the vanilla C900 cores. > >My assumption is that the same IP cores are the same unless specially >customized. Ah see that is assuming people get it right. I've been in the mindset of "what if the difference is only noticed after the DT has been shipped". I guess that's where we've been at odds. > >> >> 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? >> > > >> > >
