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xtensa: allow arch-specific arch_spin_relax() with more NOPs #60601

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Jul 20, 2023
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xtensa: allow arch-specific arch_spin_relax() with more NOPs #60601

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16 changes: 16 additions & 0 deletions arch/xtensa/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,22 @@ config XTENSA_CCOUNT_HZ
Rate in HZ of the Xtensa core as measured by the value of
the CCOUNT register.

config XTENSA_MORE_SPIN_RELAX_NOPS
bool "Use Xtensa specific arch_spin_relax() with more NOPs"
help
Some Xtensa SoCs, especially under SMP, may need extra
NOPs after failure to lock a spinlock. This gives
the bus extra time to synchronize the RCW transaction
among CPUs.

config XTENSA_NUM_SPIN_RELAX_NOPS
int "Number of NOPs to be used in arch_spin_relax()"
default 1
depends on XTENSA_MORE_SPIN_RELAX_NOPS
help
Specify the number of NOPs in Xtensa specific
arch_spin_relax().

if CPU_HAS_MMU

config XTENSA_MMU
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13 changes: 13 additions & 0 deletions arch/xtensa/core/xtensa-asm2.c
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Expand Up @@ -455,3 +455,16 @@ int z_xtensa_irq_is_enabled(unsigned int irq)

return (ie & (1 << irq)) != 0U;
}

#ifdef CONFIG_XTENSA_MORE_SPIN_RELAX_NOPS
/* Some compilers might "optimize out" (i.e. remove) continuous NOPs.
* So force no optimization to avoid that.
*/
__no_optimization
void arch_spin_relax(void)
{
#define NOP1(_, __) __asm__ volatile("nop.n;");
LISTIFY(CONFIG_XTENSA_NUM_SPIN_RELAX_NOPS, NOP1, (;))
#undef NOP1
}
#endif /* CONFIG_XTENSA_MORE_SPIN_RELAX_NOPS */
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