riscv: errata: thead: use riscv_nonstd_cache_ops for CMO #251
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Previously, we use alternative mechanism to dynamically patch the CMO operations for THEAD C906/C910 during boot for performance reason. But as pointed out by Arnd, "there is already a significant cost in accessing the invalidated cache lines afterwards, which is likely going to be much higher than the cost of an indirect branch". And indeed, there's no performance difference with GMAC and EMMC per my test on Sipeed Lichee Pi 4A board. Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify the alternative code, and to acchieve Arnd's goal -- "I think moving the THEAD ops at the same level as all nonstandard operations makes sense, but I'd still leave CMO as an explicit fast path that avoids the indirect branch. This seems like the right thing to do both for readability and for platforms on which the indirect branch has a noticeable overhead." Signed-off-by: Jisheng Zhang <jszhang@kernel.org> Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
T-HEAD CPUs such as C906/C910/C920 support phy address based CMO, use them so that we don't need to convert to virt address. Signed-off-by: Jisheng Zhang <jszhang@kernel.org> Reviewed-by: Guo Ren <guoren@kernel.org> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
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Pull request for series with
subject: riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
version: 4
url: https://patchwork.kernel.org/project/linux-riscv/list/?series=801046