Messages in this thread | | | Date | Wed, 12 Feb 2020 16:47:56 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 6/7] microblaze: Implement architecture spinlock |
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On Wed, Feb 12, 2020 at 04:42:28PM +0100, Michal Simek wrote: > From: Stefan Asserhall <stefan.asserhall@xilinx.com> > > Using exclusive loads/stores to implement spinlocks which can be used on > SMP systems. > > Signed-off-by: Stefan Asserhall <stefan.asserhall@xilinx.com> > Signed-off-by: Michal Simek <michal.simek@xilinx.com> > --- > > arch/microblaze/include/asm/spinlock.h | 240 +++++++++++++++++++ > arch/microblaze/include/asm/spinlock_types.h | 25 ++ > 2 files changed, 265 insertions(+) > create mode 100644 arch/microblaze/include/asm/spinlock.h > create mode 100644 arch/microblaze/include/asm/spinlock_types.h > > diff --git a/arch/microblaze/include/asm/spinlock.h b/arch/microblaze/include/asm/spinlock.h > new file mode 100644 > index 000000000000..0199ea9f7f0f > --- /dev/null > +++ b/arch/microblaze/include/asm/spinlock.h > @@ -0,0 +1,240 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Copyright (C) 2013-2020 Xilinx, Inc. > + */ > + > +#ifndef _ASM_MICROBLAZE_SPINLOCK_H > +#define _ASM_MICROBLAZE_SPINLOCK_H > + > +/* > + * Unlocked value: 0 > + * Locked value: 1 > + */ > +#define arch_spin_is_locked(x) (READ_ONCE((x)->lock) != 0) > + > +static inline void arch_spin_lock(arch_spinlock_t *lock) > +{ > + unsigned long tmp; > + > + __asm__ __volatile__ ( > + /* load conditional address in %1 to %0 */ > + "1: lwx %0, %1, r0;\n" > + /* not zero? try again */ > + " bnei %0, 1b;\n" > + /* increment lock by 1 */ > + " addi %0, r0, 1;\n" > + /* attempt store */ > + " swx %0, %1, r0;\n" > + /* checking msr carry flag */ > + " addic %0, r0, 0;\n" > + /* store failed (MSR[C] set)? try again */ > + " bnei %0, 1b;\n" > + /* Outputs: temp variable for load result */ > + : "=&r" (tmp) > + /* Inputs: lock address */ > + : "r" (&lock->lock) > + : "cc", "memory" > + ); > +}
That's a test-and-set spinlock if I read it correctly. Why? that's the worst possible spinlock implementation possible.
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