Commit a9ceb78bc75c (cpuidle,menu: use interactivity_req to disable polling) exposed a bug in menu_select() causing it to return -1 on systems with CPUIDLE_DRIVER_STATE_START equal to zero, although it should have returned 0. As a result, idle states are not entered by CPUs on those systems. Namely, on the systems in question data->last_state_idx is initially equal to -1 and the above commit modified the condition that would have caused it to be changed to 0 to be less likely to trigger which exposed the problem. However, setting data->last_state_idx initially to -1 doesn't make sense at all and on the affected systems it should always be set to CPUIDLE_DRIVER_STATE_START (ie. 0) unconditionally, so make that happen.
Unified · Split
| @@ -294,8 +294,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) · 293 unmodified lines | ||
| 294 | 294 | data->needs_update = 0; |
| 295 | 295 | } |
| 296 | 296 | |
| 297 | − data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1; | |
| 298 | − | |
| 299 | 297 | /* Special case when user has set very strict latency requirement */ |
| 300 | 298 | if (unlikely(latency_req == 0)) |
| 301 | 299 | return 0; |
| @@ -326,14 +324,19 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) · 24 unmodified lines | ||
| 326 | 324 | if (latency_req > interactivity_req) |
| 327 | 325 | latency_req = interactivity_req; |
| 328 | 326 | |
| 329 | − /* | |
| 330 | − * We want to default to C1 (hlt), not to busy polling | |
| 331 | − * unless the timer is happening really really soon. | |
| 332 | − */ | |
| 333 | − if (interactivity_req > 20 && | |
| 334 | − !drv->states[CPUIDLE_DRIVER_STATE_START].disabled && | |
| 335 | − dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0) | |
| 327 | + if (CPUIDLE_DRIVER_STATE_START > 0) { | |
| 328 | + data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1; | |
| 329 | + /* | |
| 330 | + * We want to default to C1 (hlt), not to busy polling | |
| 331 | + * unless the timer is happening really really soon. | |
| 332 | + */ | |
| 333 | + if (interactivity_req > 20 && | |
| 334 | + !drv->states[CPUIDLE_DRIVER_STATE_START].disabled && | |
| 335 | + dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0) | |
| 336 | + data->last_state_idx = CPUIDLE_DRIVER_STATE_START; | |
| 337 | + } else { | |
| 336 | 338 | data->last_state_idx = CPUIDLE_DRIVER_STATE_START; |
| 339 | + } | |
| 337 | 340 | |
| 338 | 341 | /* |
| 339 | 342 | * Find the idle state with the lowest power while satisfying |