On Wed, Apr 22, 2015 at 12:09:21PM -0500, Greg Bellows wrote:
> Add support for trapping WFI and WFE instructions to the proper EL when
> SCTLR/SCR/HCR settings apply.
>
> Signed-off-by: Greg Bellows <greg.bell...@linaro.org>
>
> ---
>
> v1 -> v2
> - Replace check loop with simpler if checks.
> - Changed WFx syncdrome function to take bool
> - Changed return of uint32_t to int
> - Added cdditional comments.
> ---
> target-arm/internals.h | 2 +-
> target-arm/op_helper.c | 76
> ++++++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 74 insertions(+), 4 deletions(-)
>
> diff --git a/target-arm/internals.h b/target-arm/internals.h
> index de0a9c1..8e208f7 100644
> --- a/target-arm/internals.h
> +++ b/target-arm/internals.h
> @@ -347,7 +347,7 @@ static inline uint32_t syn_breakpoint(int same_el)
> | ARM_EL_IL | 0x22;
> }
>
> -static inline uint32_t syn_wfx(int cv, int cond, int ti)
> +static inline uint32_t syn_wfx(int cv, int cond, bool ti)
> {
> return (EC_WFX_TRAP << ARM_EL_EC_SHIFT) |
> (cv << 24) | (cond << 20) | ti;
> diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
> index 971edc7..43aa8ef 100644
> --- a/target-arm/op_helper.c
> +++ b/target-arm/op_helper.c
> @@ -223,23 +223,93 @@ uint32_t HELPER(usat16)(CPUARMState *env, uint32_t x,
> uint32_t shift)
> return res;
> }
>
> +/* Function checks whether WFx (WFI/WFE) instructions are set-up to be
> trapped.
> + * The function returns the target EL (1-3) if the instruction is to be
> trapped
> + * otherwise it returns 0 indicating it is not trapped.
> + */
> +static inline int check_wfx_trap(CPUARMState *env, bool is_wfe)
> +{
> + int cur_el = arm_current_el(env);
> + uint64_t mask;
> +
> + /* If we are currently in EL0 then we need to check if SCTLR is set up
> for
> + * WFx instructions being trapped to EL1.
> + */
> + if (cur_el < 1) {
> + mask = is_wfe ? SCTLR_nTWE : SCTLR_nTWI;
> + if (arm_el_is_aa64(env, 1)) {
> + if (!(env->cp15.sctlr_el[1] & mask)) {
> + return 1;
> + }
> + } else if (arm_feature(env, ARM_FEATURE_V8)) {
> + /* SCTLR WFx SCTLR trap bits only exist in ARMv8 */
> + if (!(A32_BANKED_CURRENT_REG_GET(env, sctlr) & mask)) {
> + return 1;
> + }
> + }
> + }
> +
> + /* We are not trapping to EL1 at this point.
> + * Check if we are trapping WFx to EL2 it present.
> + */
> + if (cur_el < 2) {
> + if (arm_feature(env, ARM_FEATURE_EL2) && !arm_is_secure(env)) {
> + mask = (is_wfe) ? HCR_TWE : HCR_TWI;
> + if (env->cp15.hcr_el2 & mask) {
> + return 2;
> + }
> + }
> + }
> +
> + /* We are not trapping to EL1 or EL2 at this point.
> + * Check if we are trapping WFx to EL3 if present.
> + */
> + if (cur_el < 3) {
> + if (arm_feature(env, ARM_FEATURE_EL3) &&
> + arm_feature(env, ARM_FEATURE_V8)) {
> + mask = (is_wfe) ? SCR_TWE : SCR_TWI;
> + if (env->cp15.scr_el3 & mask) {
> + return 3;
> + }
> + }
> + }
> +
> + return 0;
> +}
> +
> void HELPER(wfi)(CPUARMState *env)
> {
> CPUState *cs = CPU(arm_env_get_cpu(env));
> + int target_el = check_wfx_trap(env, false);
>
> - cs->exception_index = EXCP_HLT;
> - cs->halted = 1;
> + if (target_el) {
> + cs->exception_index = EXCP_UDEF;
> + env->exception.syndrome = syn_wfx(1, 0xe, false);
> + env->exception.target_el = target_el;
> + env->pc -= 4;
> + } else {
> + cs->exception_index = EXCP_HLT;
> + cs->halted = 1;
> + }
> cpu_loop_exit(cs);
> }
>
> void HELPER(wfe)(CPUARMState *env)
> {
> CPUState *cs = CPU(arm_env_get_cpu(env));
> + int target_el = check_wfx_trap(env, true);
>
> /* Don't actually halt the CPU, just yield back to top
> * level loop
> */
> - cs->exception_index = EXCP_YIELD;
> + if (target_el) {
> + cs->exception_index = EXCP_UDEF;
> + env->exception.syndrome = syn_wfx(1, 0xe, true);
> + env->exception.target_el = target_el;
> + env->pc -= 4;
> + } else {
> + cs->exception_index = EXCP_YIELD;
> + }
> cpu_loop_exit(cs);
> }
Hi Greg,
Before trapping, don't you need to check that the CPU has no actual work?
e.g:
if (!cc->has_work(cs) && ..)
I think you can still EXCP_YIELD the core if it has work though as it's
probably a good place to reschedule other CPUs in our single-threaded SMP model.
Cheers,
Edgar
