forked from Minki/linux
714f599255
CPU suspend is the standard kernel interface to be used to enter
low-power states on ARM64 systems. Current cpu_suspend implementation
by default assumes that all low power states are losing the CPU context,
so the CPU registers must be saved and cleaned to DRAM upon state
entry. Furthermore, the current cpu_suspend() implementation assumes
that if the CPU suspend back-end method returns when called, this has
to be considered an error regardless of the return code (which can be
successful) since the CPU was not expected to return from a code path that
is different from cpu_resume code path - eg returning from the reset vector.
All in all this means that the current API does not cope well with low-power
states that preserve the CPU context when entered (ie retention states),
since first of all the context is saved for nothing on state entry for
those states and a successful state entry can return as a normal function
return, which is considered an error by the current CPU suspend
implementation.
This patch refactors the cpu_suspend() API so that it can be split in
two separate functionalities. The arm64 cpu_suspend API just provides
a wrapper around CPU suspend operation hook. A new function is
introduced (for architecture code use only) for states that require
context saving upon entry:
__cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
__cpu_suspend() saves the context on function entry and calls the
so called suspend finisher (ie fn) to complete the suspend operation.
The finisher is not expected to return, unless it fails in which case
the error is propagated back to the __cpu_suspend caller.
The API refactoring results in the following pseudo code call sequence for a
suspending CPU, when triggered from a kernel subsystem:
/*
* int cpu_suspend(unsigned long idx)
* @idx: idle state index
*/
{
-> cpu_suspend(idx)
|---> CPU operations suspend hook called, if present
|--> if (retention_state)
|--> direct suspend back-end call (eg PSCI suspend)
else
|--> __cpu_suspend(idx, &back_end_finisher);
}
By refactoring the cpu_suspend API this way, the CPU operations back-end
has a chance to detect whether idle states require state saving or not
and can call the required suspend operations accordingly either through
simple function call or indirectly through __cpu_suspend() which carries out
state saving and suspend finisher dispatching to complete idle state entry.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
151 lines
4.2 KiB
C
151 lines
4.2 KiB
C
#include <linux/percpu.h>
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#include <linux/slab.h>
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#include <asm/cacheflush.h>
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#include <asm/cpu_ops.h>
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#include <asm/debug-monitors.h>
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#include <asm/pgtable.h>
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#include <asm/memory.h>
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#include <asm/smp_plat.h>
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#include <asm/suspend.h>
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#include <asm/tlbflush.h>
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extern int __cpu_suspend_enter(unsigned long arg, int (*fn)(unsigned long));
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/*
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* This is called by __cpu_suspend_enter() to save the state, and do whatever
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* flushing is required to ensure that when the CPU goes to sleep we have
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* the necessary data available when the caches are not searched.
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*
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* ptr: CPU context virtual address
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* save_ptr: address of the location where the context physical address
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* must be saved
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*/
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void notrace __cpu_suspend_save(struct cpu_suspend_ctx *ptr,
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phys_addr_t *save_ptr)
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{
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*save_ptr = virt_to_phys(ptr);
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cpu_do_suspend(ptr);
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/*
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* Only flush the context that must be retrieved with the MMU
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* off. VA primitives ensure the flush is applied to all
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* cache levels so context is pushed to DRAM.
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*/
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__flush_dcache_area(ptr, sizeof(*ptr));
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__flush_dcache_area(save_ptr, sizeof(*save_ptr));
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}
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/*
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* This hook is provided so that cpu_suspend code can restore HW
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* breakpoints as early as possible in the resume path, before reenabling
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* debug exceptions. Code cannot be run from a CPU PM notifier since by the
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* time the notifier runs debug exceptions might have been enabled already,
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* with HW breakpoints registers content still in an unknown state.
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*/
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void (*hw_breakpoint_restore)(void *);
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void __init cpu_suspend_set_dbg_restorer(void (*hw_bp_restore)(void *))
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{
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/* Prevent multiple restore hook initializations */
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if (WARN_ON(hw_breakpoint_restore))
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return;
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hw_breakpoint_restore = hw_bp_restore;
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}
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/**
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* cpu_suspend() - function to enter a low-power state
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* @arg: argument to pass to CPU suspend operations
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*
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* Return: 0 on success, -EOPNOTSUPP if CPU suspend hook not initialized, CPU
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* operations back-end error code otherwise.
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*/
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int cpu_suspend(unsigned long arg)
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{
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int cpu = smp_processor_id();
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/*
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* If cpu_ops have not been registered or suspend
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* has not been initialized, cpu_suspend call fails early.
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*/
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if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_suspend)
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return -EOPNOTSUPP;
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return cpu_ops[cpu]->cpu_suspend(arg);
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}
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/*
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* __cpu_suspend
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*
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* arg: argument to pass to the finisher function
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* fn: finisher function pointer
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*
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*/
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int __cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
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{
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struct mm_struct *mm = current->active_mm;
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int ret;
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unsigned long flags;
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/*
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* From this point debug exceptions are disabled to prevent
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* updates to mdscr register (saved and restored along with
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* general purpose registers) from kernel debuggers.
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*/
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local_dbg_save(flags);
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/*
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* mm context saved on the stack, it will be restored when
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* the cpu comes out of reset through the identity mapped
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* page tables, so that the thread address space is properly
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* set-up on function return.
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*/
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ret = __cpu_suspend_enter(arg, fn);
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if (ret == 0) {
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cpu_switch_mm(mm->pgd, mm);
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flush_tlb_all();
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/*
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* Restore per-cpu offset before any kernel
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* subsystem relying on it has a chance to run.
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*/
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set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
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/*
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* Restore HW breakpoint registers to sane values
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* before debug exceptions are possibly reenabled
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* through local_dbg_restore.
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*/
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if (hw_breakpoint_restore)
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hw_breakpoint_restore(NULL);
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}
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/*
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* Restore pstate flags. OS lock and mdscr have been already
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* restored, so from this point onwards, debugging is fully
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* renabled if it was enabled when core started shutdown.
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*/
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local_dbg_restore(flags);
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return ret;
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}
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extern struct sleep_save_sp sleep_save_sp;
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extern phys_addr_t sleep_idmap_phys;
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static int __init cpu_suspend_init(void)
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{
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void *ctx_ptr;
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/* ctx_ptr is an array of physical addresses */
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ctx_ptr = kcalloc(mpidr_hash_size(), sizeof(phys_addr_t), GFP_KERNEL);
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if (WARN_ON(!ctx_ptr))
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return -ENOMEM;
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sleep_save_sp.save_ptr_stash = ctx_ptr;
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sleep_save_sp.save_ptr_stash_phys = virt_to_phys(ctx_ptr);
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sleep_idmap_phys = virt_to_phys(idmap_pg_dir);
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__flush_dcache_area(&sleep_save_sp, sizeof(struct sleep_save_sp));
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__flush_dcache_area(&sleep_idmap_phys, sizeof(sleep_idmap_phys));
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return 0;
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}
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early_initcall(cpu_suspend_init);
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