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

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This adds a Kconfig to introduce the Xtensa specific
arch_spin_relax() which can do more NOPs. Some Xtensa SoCs
may need more NOPs after failure to lock a spinlock,
especially under SMP. This gives the bus extra time to
propagate the RCW transactions among CPUs.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
This commit is contained in:
Daniel Leung 2023-07-18 17:44:58 -07:00 • committed by Fabio Baltieri
commit a458d0443a
2 changed files with 29 additions and 0 deletions
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16
arch/xtensa/Kconfig
View file

@ -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

13
arch/xtensa/core/xtensa-asm2.c
View file

@ -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 */