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6ad2a661ff
Put the barrier() before the OP so that anything we read out in
OP and check in COND will actually be read out after the timeout
has been evaluated.
Currently the only place where we use OP is __intel_wait_for_register(),
but the use there is precisely susceptible to this reordering, assuming
the ktime_*() stuff itself doesn't act as a sufficient barrier:
__intel_wait_for_register(...)
{
...
ret = __wait_for(reg_value = intel_uncore_read_notrace(...),
(reg_value & mask) == value, ...);
...
}
Cc: stable@vger.kernel.org
Fixes: 1c3c1dc66a ("drm/i915: Add compiler barrier to wait_for")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260313110740.24620-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit a464bace04)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
120 lines
3.2 KiB
C
120 lines
3.2 KiB
C
/* SPDX-License-Identifier: MIT */
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/* Copyright © 2025 Intel Corporation */
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#ifndef __I915_WAIT_UTIL_H__
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#define __I915_WAIT_UTIL_H__
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#include <linux/compiler.h>
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#include <linux/delay.h>
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#include <linux/ktime.h>
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#include <linux/sched/clock.h>
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#include <linux/smp.h>
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/*
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* __wait_for - magic wait macro
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*
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* Macro to help avoid open coding check/wait/timeout patterns. Note that it's
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* important that we check the condition again after having timed out, since the
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* timeout could be due to preemption or similar and we've never had a chance to
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* check the condition before the timeout.
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*/
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#define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
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const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
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long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
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int ret__; \
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might_sleep(); \
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for (;;) { \
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const bool expired__ = ktime_after(ktime_get_raw(), end__); \
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/* Guarantee COND check prior to timeout */ \
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barrier(); \
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OP; \
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if (COND) { \
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ret__ = 0; \
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break; \
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} \
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if (expired__) { \
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ret__ = -ETIMEDOUT; \
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break; \
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} \
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usleep_range(wait__, wait__ * 2); \
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if (wait__ < (Wmax)) \
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wait__ <<= 1; \
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} \
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ret__; \
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})
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#define _wait_for(COND, US, Wmin, Wmax) __wait_for(, (COND), (US), (Wmin), \
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(Wmax))
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#define wait_for(COND, MS) _wait_for((COND), (MS) * 1000, 10, 1000)
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/*
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* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false.
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* On PREEMPT_RT the context isn't becoming atomic because it is used in an
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* interrupt handler or because a spinlock_t is acquired. This leads to
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* warnings which don't occur otherwise and therefore the check is disabled.
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*/
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#if IS_ENABLED(CONFIG_DRM_I915_DEBUG) && IS_ENABLED(CONFIG_PREEMPT_COUNT) && !defined(CONFIG_PREEMPT_RT)
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# define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic())
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#else
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# define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)
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#endif
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#define _wait_for_atomic(COND, US, ATOMIC) \
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({ \
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int cpu, ret, timeout = (US) * 1000; \
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u64 base; \
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_WAIT_FOR_ATOMIC_CHECK(ATOMIC); \
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if (!(ATOMIC)) { \
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preempt_disable(); \
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cpu = smp_processor_id(); \
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} \
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base = local_clock(); \
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for (;;) { \
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u64 now = local_clock(); \
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if (!(ATOMIC)) \
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preempt_enable(); \
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/* Guarantee COND check prior to timeout */ \
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barrier(); \
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if (COND) { \
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ret = 0; \
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break; \
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} \
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if (now - base >= timeout) { \
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ret = -ETIMEDOUT; \
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break; \
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} \
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cpu_relax(); \
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if (!(ATOMIC)) { \
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preempt_disable(); \
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if (unlikely(cpu != smp_processor_id())) { \
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timeout -= now - base; \
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cpu = smp_processor_id(); \
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base = local_clock(); \
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} \
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} \
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} \
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ret; \
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})
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#define wait_for_us(COND, US) \
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({ \
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int ret__; \
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BUILD_BUG_ON(!__builtin_constant_p(US)); \
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if ((US) > 10) \
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ret__ = _wait_for((COND), (US), 10, 10); \
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else \
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ret__ = _wait_for_atomic((COND), (US), 0); \
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ret__; \
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})
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#define wait_for_atomic_us(COND, US) \
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({ \
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BUILD_BUG_ON(!__builtin_constant_p(US)); \
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BUILD_BUG_ON((US) > 50000); \
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_wait_for_atomic((COND), (US), 1); \
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})
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#define wait_for_atomic(COND, MS) wait_for_atomic_us((COND), (MS) * 1000)
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#endif /* __I915_WAIT_UTIL_H__ */
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