On Tue, Apr 19, 2022 at 12:22:12PM +0100, Mark Brown wrote: > +* There are a number of optional SME features, presence of these is reported > + through AT_HWCAP2 through: > + > + HWCAP2_SME_I16I64 > + HWCAP2_SME_F64F64 > + HWCAP2_SME_I8I32 > + HWCAP2_SME_F16F32 > + HWCAP2_SME_B16F32 > + HWCAP2_SME_F32F32 > + HWCAP2_SME_FA64 Marc pointed out that in combination with FEAT_WFxT, we used all the HWCAP2 bits (32). While we are ok for now, we'll soon need to look into what to do when the next features turn up. Some options: 1. Only provide HWCAP2_SME and let the ID_AA64SMFR0_EL1 features be probed via MRS emulation. It doesn't solve the problem but it buys us a bit of time. 2. Don't bother with any new HWCAPs, just rely on MRS emulation (we have HWCAP_CPUID advertising this). 3. Start using the upper 32-bit of HWCAP and HWCAP2 (we initially didn't go into these as there was a slight chance of merging ILP32). Does the libc rely on the upper bits for anything? Or does it just assume a 32-bit HWCAPs layout? 4. Introduce HWCAP3. Szabolcs, any thoughts? Thanks. -- Catalin
