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122 lines
3.0 KiB
122 lines
3.0 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* Count register synchronisation. |
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* |
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* All CPUs will have their count registers synchronised to the CPU0 next time |
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* value. This can cause a small timewarp for CPU0. All other CPU's should |
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* not have done anything significant (but they may have had interrupts |
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* enabled briefly - prom_smp_finish() should not be responsible for enabling |
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* interrupts...) |
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*/ |
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#include <linux/kernel.h> |
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#include <linux/irqflags.h> |
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#include <linux/cpumask.h> |
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#include <asm/r4k-timer.h> |
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#include <linux/atomic.h> |
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#include <asm/barrier.h> |
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#include <asm/mipsregs.h> |
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static unsigned int initcount = 0; |
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static atomic_t count_count_start = ATOMIC_INIT(0); |
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static atomic_t count_count_stop = ATOMIC_INIT(0); |
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#define COUNTON 100 |
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#define NR_LOOPS 3 |
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void synchronise_count_master(int cpu) |
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{ |
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int i; |
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unsigned long flags; |
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pr_info("Synchronize counters for CPU %u: ", cpu); |
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local_irq_save(flags); |
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/* |
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* We loop a few times to get a primed instruction cache, |
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* then the last pass is more or less synchronised and |
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* the master and slaves each set their cycle counters to a known |
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* value all at once. This reduces the chance of having random offsets |
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* between the processors, and guarantees that the maximum |
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* delay between the cycle counters is never bigger than |
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* the latency of information-passing (cachelines) between |
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* two CPUs. |
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*/ |
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for (i = 0; i < NR_LOOPS; i++) { |
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/* slaves loop on '!= 2' */ |
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while (atomic_read(&count_count_start) != 1) |
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mb(); |
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atomic_set(&count_count_stop, 0); |
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smp_wmb(); |
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/* Let the slave writes its count register */ |
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atomic_inc(&count_count_start); |
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/* Count will be initialised to current timer */ |
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if (i == 1) |
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initcount = read_c0_count(); |
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/* |
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* Everyone initialises count in the last loop: |
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*/ |
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if (i == NR_LOOPS-1) |
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write_c0_count(initcount); |
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/* |
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* Wait for slave to leave the synchronization point: |
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*/ |
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while (atomic_read(&count_count_stop) != 1) |
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mb(); |
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atomic_set(&count_count_start, 0); |
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smp_wmb(); |
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atomic_inc(&count_count_stop); |
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} |
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/* Arrange for an interrupt in a short while */ |
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write_c0_compare(read_c0_count() + COUNTON); |
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local_irq_restore(flags); |
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/* |
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* i386 code reported the skew here, but the |
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* count registers were almost certainly out of sync |
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* so no point in alarming people |
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*/ |
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pr_cont("done.\n"); |
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} |
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void synchronise_count_slave(int cpu) |
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{ |
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int i; |
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unsigned long flags; |
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local_irq_save(flags); |
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/* |
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* Not every cpu is online at the time this gets called, |
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* so we first wait for the master to say everyone is ready |
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*/ |
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for (i = 0; i < NR_LOOPS; i++) { |
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atomic_inc(&count_count_start); |
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while (atomic_read(&count_count_start) != 2) |
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mb(); |
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/* |
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* Everyone initialises count in the last loop: |
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*/ |
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if (i == NR_LOOPS-1) |
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write_c0_count(initcount); |
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atomic_inc(&count_count_stop); |
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while (atomic_read(&count_count_stop) != 2) |
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mb(); |
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} |
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/* Arrange for an interrupt in a short while */ |
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write_c0_compare(read_c0_count() + COUNTON); |
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local_irq_restore(flags); |
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} |
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#undef NR_LOOPS
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