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This is the core code implementing big.LITTLE switcher functionality. Rationale for this code is available here: http://lwn.net/Articles/481055/ The main entry point for a switch request is: void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id) If the calling CPU is not the wanted one, this wrapper takes care of sending the request to the appropriate CPU with schedule_work_on(). At the moment the core switch operation is handled by bL_switch_to() which must be called on the CPU for which a switch is requested. What this code does: * Return early if the current cluster is the wanted one. * Close the gate in the kernel entry vector for both the inbound and outbound CPUs. * Wake up the inbound CPU so it can perform its reset sequence in parallel up to the kernel entry vector gate. * Migrate all interrupts in the GIC targeting the outbound CPU interface to the inbound CPU interface, including SGIs. This is performed by gic_migrate_target() in drivers/irqchip/irq-gic.c. * Call cpu_pm_enter() which takes care of flushing the VFP state to RAM and save the CPU interface config from the GIC to RAM. * Modify the cpu_logical_map to refer to the inbound physical CPU. * Call cpu_suspend() which saves the CPU state (general purpose registers, page table address) onto the stack and store the resulting stack pointer in an array indexed by the updated cpu_logical_map, then call the provided shutdown function. This happens in arch/arm/kernel/sleep.S. At this point, the provided shutdown function executed by the outbound CPU ungates the inbound CPU. Therefore the inbound CPU: * Picks up the saved stack pointer in the array indexed by its MPIDR in arch/arm/kernel/sleep.S. * The MMU and caches are re-enabled using the saved state on the provided stack, just like if this was a resume operation from a suspended state. * Then cpu_suspend() returns, although this is on the inbound CPU rather than the outbound CPU which called it initially. * The function cpu_pm_exit() is called which effect is to restore the CPU interface state in the GIC using the state previously saved by the outbound CPU. * Exit of bL_switch_to() to resume normal kernel execution on the new CPU. However, the outbound CPU is potentially still running in parallel while the inbound CPU is resuming normal kernel execution, hence we need per CPU stack isolation to execute bL_do_switch(). After the outbound CPU has ungated the inbound CPU, it calls mcpm_cpu_power_down() to: * Clean its L1 cache. * If it is the last CPU still alive in its cluster (last man standing), it also cleans its L2 cache and disables cache snooping from the other cluster. * Power down the CPU (or whole cluster). Code called from bL_do_switch() might end up referencing 'current' for some reasons. However, 'current' is derived from the stack pointer. With any arbitrary stack, the returned value for 'current' and any dereferenced values through it are just random garbage which may lead to segmentation faults. The active page table during the execution of bL_do_switch() is also a problem. There is no guarantee that the inbound CPU won't destroy the corresponding task which would free the attached page table while the outbound CPU is still running and relying on it. To solve both issues, we borrow some of the task space belonging to the init/idle task which, by its nature, is lightly used and therefore is unlikely to clash with our usage. The init task is also never going away. Right now the logical CPU number is assumed to be equivalent to the physical CPU number within each cluster. The kernel should also be booted with only one cluster active. These limitations will be lifted eventually. Signed-off-by: Nicolas Pitre <nico@linaro.org> |
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| .. | ||
| bL_switcher.c | ||
| dmabounce.c | ||
| edma.c | ||
| firmware.c | ||
| icst.c | ||
| it8152.c | ||
| Kconfig | ||
| locomo.c | ||
| Makefile | ||
| mcpm_entry.c | ||
| mcpm_head.S | ||
| mcpm_platsmp.c | ||
| sa1111.c | ||
| scoop.c | ||
| sharpsl_param.c | ||
| timer-sp.c | ||
| via82c505.c | ||
| vlock.h | ||
| vlock.S | ||