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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /arch/mips/kernel/sync-r4k.c | |
parent | Initial commit. (diff) | |
download | linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip |
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/mips/kernel/sync-r4k.c')
-rw-r--r-- | arch/mips/kernel/sync-r4k.c | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/arch/mips/kernel/sync-r4k.c b/arch/mips/kernel/sync-r4k.c new file mode 100644 index 000000000..abdd7aaa3 --- /dev/null +++ b/arch/mips/kernel/sync-r4k.c @@ -0,0 +1,122 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Count register synchronisation. + * + * All CPUs will have their count registers synchronised to the CPU0 next time + * value. This can cause a small timewarp for CPU0. All other CPU's should + * not have done anything significant (but they may have had interrupts + * enabled briefly - prom_smp_finish() should not be responsible for enabling + * interrupts...) + */ + +#include <linux/kernel.h> +#include <linux/irqflags.h> +#include <linux/cpumask.h> + +#include <asm/r4k-timer.h> +#include <linux/atomic.h> +#include <asm/barrier.h> +#include <asm/mipsregs.h> + +static unsigned int initcount = 0; +static atomic_t count_count_start = ATOMIC_INIT(0); +static atomic_t count_count_stop = ATOMIC_INIT(0); + +#define COUNTON 100 +#define NR_LOOPS 3 + +void synchronise_count_master(int cpu) +{ + int i; + unsigned long flags; + + pr_info("Synchronize counters for CPU %u: ", cpu); + + local_irq_save(flags); + + /* + * We loop a few times to get a primed instruction cache, + * then the last pass is more or less synchronised and + * the master and slaves each set their cycle counters to a known + * value all at once. This reduces the chance of having random offsets + * between the processors, and guarantees that the maximum + * delay between the cycle counters is never bigger than + * the latency of information-passing (cachelines) between + * two CPUs. + */ + + for (i = 0; i < NR_LOOPS; i++) { + /* slaves loop on '!= 2' */ + while (atomic_read(&count_count_start) != 1) + mb(); + atomic_set(&count_count_stop, 0); + smp_wmb(); + + /* Let the slave writes its count register */ + atomic_inc(&count_count_start); + + /* Count will be initialised to current timer */ + if (i == 1) + initcount = read_c0_count(); + + /* + * Everyone initialises count in the last loop: + */ + if (i == NR_LOOPS-1) + write_c0_count(initcount); + + /* + * Wait for slave to leave the synchronization point: + */ + while (atomic_read(&count_count_stop) != 1) + mb(); + atomic_set(&count_count_start, 0); + smp_wmb(); + atomic_inc(&count_count_stop); + } + /* Arrange for an interrupt in a short while */ + write_c0_compare(read_c0_count() + COUNTON); + + local_irq_restore(flags); + + /* + * i386 code reported the skew here, but the + * count registers were almost certainly out of sync + * so no point in alarming people + */ + pr_cont("done.\n"); +} + +void synchronise_count_slave(int cpu) +{ + int i; + unsigned long flags; + + local_irq_save(flags); + + /* + * Not every cpu is online at the time this gets called, + * so we first wait for the master to say everyone is ready + */ + + for (i = 0; i < NR_LOOPS; i++) { + atomic_inc(&count_count_start); + while (atomic_read(&count_count_start) != 2) + mb(); + + /* + * Everyone initialises count in the last loop: + */ + if (i == NR_LOOPS-1) + write_c0_count(initcount); + + atomic_inc(&count_count_stop); + while (atomic_read(&count_count_stop) != 2) + mb(); + } + /* Arrange for an interrupt in a short while */ + write_c0_compare(read_c0_count() + COUNTON); + + local_irq_restore(flags); +} +#undef NR_LOOPS |