riscv: Apply Zawrs when available #172
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If we're going to provide the encoding for 'pause' in cpu_relax() anyway, then we can drop the toolchain checks and just always use it. The advantage of doing this is that other code that need pause don't need to also define it (yes, another use is coming). Add the definition to insn-def.h since it's an instruction definition and also because insn-def.h doesn't include much, so it's safe to include from asm/vdso/processor.h without concern for circular dependencies. Signed-off-by: Andrew Jones <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Palmer Dabbelt <[email protected]> Signed-off-by: Chen Pei <[email protected]>
Add description for the Zawrs (Wait-on-Reservation-Set) ISA extension which was ratified of riscv-isa-manual. Signed-off-by: Andrew Jones <[email protected]> Acked-by: Conor Dooley <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Palmer Dabbelt <[email protected]> Signed-off-by: Chen Pei <[email protected]>
RISC-V code uses the generic ticket lock implementation, which calls the macros smp_cond_load_relaxed() and smp_cond_load_acquire(). Introduce a RISC-V specific implementation of smp_cond_load_relaxed() which applies WRS.NTO of the Zawrs extension in order to reduce power consumption while waiting and allows hypervisors to enable guests to trap while waiting. smp_cond_load_acquire() doesn't need a RISC-V specific implementation as the generic implementation is based on smp_cond_load_relaxed() and smp_acquire__after_ctrl_dep() sufficiently provides the acquire semantics. This implementation is heavily based on Arm's approach which is the approach Andrea Parri also suggested. The Zawrs specification can be found here: https://github.com/riscv/riscv-zawrs/blob/main/zawrs.adoc Signed-off-by: Christoph Müllner <[email protected]> Co-developed-by: Andrew Jones <[email protected]> Signed-off-by: Andrew Jones <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Palmer Dabbelt <[email protected]> Signed-off-by: Chen Pei <[email protected]>
Kconfig: If the toolchain or cpu does not support the zawrs extension we should not enable it. th1520_defconfig: Enable CONFIG_JUMP_LABEL to optimize performance and resolve compilation errors. Signed-off-by: Chen Pei <[email protected]>
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These patches come from the upstream community to support zawrs extension.
The latest XuanTie C920 processor supports this extension.
Link: https://lore.kernel.org/all/[email protected]/