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coresight: Change device mode to atomic type 

The device mode is defined as local type. This type cannot promise
SMP-safe access.

Change to atomic type and impose relax ordering, which ensures the
SMP-safe synchronisation and the ordering between the mode setting and
relevant operations.

Fixes: 22fd532eaa ("coresight: etm3x: adding operation mode for etm_enable()")
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251111-arm_coresight_power_management_fix-v6-1-f55553b6c8b3@arm.com
pull/1354/merge
Leo Yan 2025-11-11 18:58:35 +00:00 committed by Suzuki K Poulose
parent b139702a88
commit 693d1eaca9
1 changed files with 11 additions and 14 deletions
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25
include/linux/coresight.h
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@ -251,15 +251,11 @@ struct coresight_trace_id_map {
* by @coresight_ops.
* @access: Device i/o access abstraction for this device.
* @dev: The device entity associated to this component.
* @mode: This tracer's mode, i.e sysFS, Perf or disabled. This is
* actually an 'enum cs_mode', but is stored in an atomic type.
* This is always accessed through local_read() and local_set(),
* but wherever it's done from within the Coresight device's lock,
* a non-atomic read would also work. This is the main point of
* synchronisation between code happening inside the sysfs mode's
* coresight_mutex and outside when running in Perf mode. A compare
* and exchange swap is done to atomically claim one mode or the
* other.
* @mode: The device mode, i.e sysFS, Perf or disabled. This is actually
* an 'enum cs_mode' but stored in an atomic type. Access is always
* through atomic APIs, ensuring SMP-safe synchronisation between
* racing from sysFS and Perf mode. A compare-and-exchange
* operation is done to atomically claim one mode or the other.
* @refcnt: keep track of what is in use. Only access this outside of the
* device's spinlock when the coresight_mutex held and mode ==
* CS_MODE_SYSFS. Otherwise it must be accessed from inside the
@ -288,7 +284,7 @@ struct coresight_device {
const struct coresight_ops *ops;
struct csdev_access access;
struct device dev;
local_t mode;
atomic_t mode;
int refcnt;
bool orphan;
/* sink specific fields */
@ -624,13 +620,14 @@ static inline bool coresight_is_percpu_sink(struct coresight_device *csdev)
static inline bool coresight_take_mode(struct coresight_device *csdev,
enum cs_mode new_mode)
{
return local_cmpxchg(&csdev->mode, CS_MODE_DISABLED, new_mode) ==
CS_MODE_DISABLED;
int curr = CS_MODE_DISABLED;
return atomic_try_cmpxchg_acquire(&csdev->mode, &curr, new_mode);
}
static inline enum cs_mode coresight_get_mode(struct coresight_device *csdev)
{
return local_read(&csdev->mode);
return atomic_read_acquire(&csdev->mode);
}
static inline void coresight_set_mode(struct coresight_device *csdev,
@ -646,7 +643,7 @@ static inline void coresight_set_mode(struct coresight_device *csdev,
WARN(new_mode != CS_MODE_DISABLED && current_mode != CS_MODE_DISABLED &&
current_mode != new_mode, "Device already in use\n");
local_set(&csdev->mode, new_mode);
atomic_set_release(&csdev->mode, new_mode);
}
struct coresight_device *coresight_register(struct coresight_desc *desc);