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asm-generic/mmiowb: Add generic implementation of mmiowb() tracking 

In preparation for removing all explicit mmiowb() calls from driver
code, implement a tracking system in asm-generic based loosely on the
PowerPC implementation. This allows architectures with a non-empty
mmiowb() definition to have the barrier automatically inserted in
spin_unlock() following a critical section containing an I/O write.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2019-02-22 12:48:44 +00:00
parent 4614bbdee3
commit d1be6a28b1
4 changed files with 89 additions and 0 deletions
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63
include/asm-generic/mmiowb.h Normal file
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@ -0,0 +1,63 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_GENERIC_MMIOWB_H
#define __ASM_GENERIC_MMIOWB_H
/*
* Generic implementation of mmiowb() tracking for spinlocks.
*
* If your architecture doesn't ensure that writes to an I/O peripheral
* within two spinlocked sections on two different CPUs are seen by the
* peripheral in the order corresponding to the lock handover, then you
* need to follow these FIVE easy steps:
*
* 1. Implement mmiowb() (and arch_mmiowb_state() if you're fancy)
* in asm/mmiowb.h, then #include this file
* 2. Ensure your I/O write accessors call mmiowb_set_pending()
* 3. Select ARCH_HAS_MMIOWB
* 4. Untangle the resulting mess of header files
* 5. Complain to your architects
*/
#ifdef CONFIG_MMIOWB
#include <linux/compiler.h>
#include <asm-generic/mmiowb_types.h>
#ifndef arch_mmiowb_state
#include <asm/percpu.h>
#include <asm/smp.h>
DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state);
#define __mmiowb_state() this_cpu_ptr(&__mmiowb_state)
#else
#define __mmiowb_state() arch_mmiowb_state()
#endif /* arch_mmiowb_state */
static inline void mmiowb_set_pending(void)
{
struct mmiowb_state *ms = __mmiowb_state();
ms->mmiowb_pending = ms->nesting_count;
}
static inline void mmiowb_spin_lock(void)
{
struct mmiowb_state *ms = __mmiowb_state();
ms->nesting_count++;
}
static inline void mmiowb_spin_unlock(void)
{
struct mmiowb_state *ms = __mmiowb_state();
if (unlikely(ms->mmiowb_pending)) {
ms->mmiowb_pending = 0;
mmiowb();
}
ms->nesting_count--;
}
#else
#define mmiowb_set_pending() do { } while (0)
#define mmiowb_spin_lock() do { } while (0)
#define mmiowb_spin_unlock() do { } while (0)
#endif /* CONFIG_MMIOWB */
#endif /* __ASM_GENERIC_MMIOWB_H */

12
include/asm-generic/mmiowb_types.h Normal file
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@ -0,0 +1,12 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_GENERIC_MMIOWB_TYPES_H
#define __ASM_GENERIC_MMIOWB_TYPES_H
#include <linux/types.h>
struct mmiowb_state {
u16 nesting_count;
u16 mmiowb_pending;
};
#endif /* __ASM_GENERIC_MMIOWB_TYPES_H */

7
kernel/Kconfig.locks
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@ -251,3 +251,10 @@ config ARCH_USE_QUEUED_RWLOCKS
config QUEUED_RWLOCKS
def_bool y if ARCH_USE_QUEUED_RWLOCKS
depends on SMP
config ARCH_HAS_MMIOWB
bool
config MMIOWB
def_bool y if ARCH_HAS_MMIOWB
depends on SMP

7
kernel/locking/spinlock.c
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@ -22,6 +22,13 @@
#include <linux/debug_locks.h>
#include <linux/export.h>
#ifdef CONFIG_MMIOWB
#ifndef arch_mmiowb_state
DEFINE_PER_CPU(struct mmiowb_state, __mmiowb_state);
EXPORT_PER_CPU_SYMBOL(__mmiowb_state);
#endif
#endif
/*
* If lockdep is enabled then we use the non-preemption spin-ops
* even on CONFIG_PREEMPT, because lockdep assumes that interrupts are