On Mon, Dec 13, 2021 at 3:27 PM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote: > > On Mon, Dec 6, 2021 at 7:28 AM Rob Herring <robh@xxxxxxxxxx> wrote: > > > > On Fri, Dec 03, 2021 at 04:20:32PM -0800, Atish Patra wrote: > > > Currently, sparse hartid is not supported for Linux RISC-V for the following > > > reasons. > > > 1. Both spinwait and ordered booting method uses __cpu_up_stack/task_pointer > > > which is an array size of NR_CPUs. > > > 2. During early booting, any hartid greater than NR_CPUs are not booted at all. > > > 3. riscv_cpuid_to_hartid_mask uses struct cpumask for generating hartid bitmap. > > > 4. SBI v0.2 implementation uses NR_CPUs as the maximum hartid number while > > > generating hartmask. > > > > > > In order to support sparse hartid, the hartid & NR_CPUS needs to be disassociated > > > which was logically incorrect anyways. NR_CPUs represent the maximum logical| > > > CPU id configured in the kernel while the hartid represent the physical hartid > > > stored in mhartid CSR defined by the privilege specification. Thus, hartid > > > can have much greater value than logical cpuid. > > > > We already have a couple of architectures with logical to physical CPU > > id maps. See cpu_logical_map. Can we make that common and use it here? > > Yes. We can move the cpu_logical_map(which is a macro) & > __cpu_logical_map(actual array with NR_CPUS size) > to common code so that all the architecture can use it instead of > defining it separately. IIRC, the macro is what varies by arch and I would move to static inlines rather than supporting: cpu_logical_map(cpu) = 0xdeadbeef; > > > That would also possibly allow for common populating the map from DT. > > > > I didn't understand this part. The mapping is populated at run time > [1] as the boot cpu can be any hart in RISC-V. > That booting hart will be mapped to cpu 0. All others will be mapped > based on how the cpu node is laid out in the DT. > Do you mean we can move the 2nd part to common code as well ? Yes, as the DT platforms just loop thru the cpu nodes and fill the logical map based on 'reg', I don't think that needs to be per arch once we have a common map. But not asking for that now. Rob
