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staging: vchiq: use completions instead of semaphores
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It is preferred in the kernel to avoid using semaphores to wait for
events, as they are optimised for the opposite situation; where the
common case is that they are available and may block only occasionally.
FYI see this thread: https://lkml.org/lkml/2008/4/11/323.

Also completions are semantically more explicit in this case.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Nicolas Saenz Julienne authored and Greg Kroah-Hartman committed Nov 27, 2018
1 parent 51c0712 commit f27e47b
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Showing 5 changed files with 106 additions and 102 deletions.
60 changes: 32 additions & 28 deletions drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/bug.h>
#include <linux/semaphore.h>
#include <linux/completion.h>
#include <linux/list.h>
#include <linux/of.h>
#include <linux/platform_device.h>
Expand Down Expand Up @@ -121,9 +121,9 @@ typedef struct user_service_struct {
int message_available_pos;
int msg_insert;
int msg_remove;
struct semaphore insert_event;
struct semaphore remove_event;
struct semaphore close_event;
struct completion insert_event;
struct completion remove_event;
struct completion close_event;
VCHIQ_HEADER_T * msg_queue[MSG_QUEUE_SIZE];
} USER_SERVICE_T;

Expand All @@ -138,8 +138,8 @@ struct vchiq_instance_struct {
VCHIQ_COMPLETION_DATA_T completions[MAX_COMPLETIONS];
int completion_insert;
int completion_remove;
struct semaphore insert_event;
struct semaphore remove_event;
struct completion insert_event;
struct completion remove_event;
struct mutex completion_mutex;

int connected;
Expand Down Expand Up @@ -562,7 +562,8 @@ add_completion(VCHIQ_INSTANCE_T instance, VCHIQ_REASON_T reason,
vchiq_log_trace(vchiq_arm_log_level,
"%s - completion queue full", __func__);
DEBUG_COUNT(COMPLETION_QUEUE_FULL_COUNT);
if (down_interruptible(&instance->remove_event) != 0) {
if (wait_for_completion_interruptible(
&instance->remove_event)) {
vchiq_log_info(vchiq_arm_log_level,
"service_callback interrupted");
return VCHIQ_RETRY;
Expand Down Expand Up @@ -600,7 +601,7 @@ add_completion(VCHIQ_INSTANCE_T instance, VCHIQ_REASON_T reason,
insert++;
instance->completion_insert = insert;

up(&instance->insert_event);
complete(&instance->insert_event);

return VCHIQ_SUCCESS;
}
Expand Down Expand Up @@ -673,7 +674,8 @@ service_callback(VCHIQ_REASON_T reason, VCHIQ_HEADER_T *header,
}

DEBUG_TRACE(SERVICE_CALLBACK_LINE);
if (down_interruptible(&user_service->remove_event)
if (wait_for_completion_interruptible(
&user_service->remove_event)
!= 0) {
vchiq_log_info(vchiq_arm_log_level,
"%s interrupted", __func__);
Expand Down Expand Up @@ -705,7 +707,7 @@ service_callback(VCHIQ_REASON_T reason, VCHIQ_HEADER_T *header,
}

spin_unlock(&msg_queue_spinlock);
up(&user_service->insert_event);
complete(&user_service->insert_event);

header = NULL;
}
Expand Down Expand Up @@ -745,7 +747,7 @@ static void close_delivered(USER_SERVICE_T *user_service)
unlock_service(user_service->service);

/* Wake the user-thread blocked in close_ or remove_service */
up(&user_service->close_event);
complete(&user_service->close_event);

user_service->close_pending = 0;
}
Expand Down Expand Up @@ -867,7 +869,7 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
if (status == VCHIQ_SUCCESS) {
/* Wake the completion thread and ask it to exit */
instance->closing = 1;
up(&instance->insert_event);
complete(&instance->insert_event);
}

break;
Expand Down Expand Up @@ -948,9 +950,9 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
instance->completion_remove - 1;
user_service->msg_insert = 0;
user_service->msg_remove = 0;
sema_init(&user_service->insert_event, 0);
sema_init(&user_service->remove_event, 0);
sema_init(&user_service->close_event, 0);
init_completion(&user_service->insert_event);
init_completion(&user_service->remove_event);
init_completion(&user_service->close_event);

if (args.is_open) {
status = vchiq_open_service_internal
Expand Down Expand Up @@ -1007,7 +1009,8 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
has been closed until the client library calls the
CLOSE_DELIVERED ioctl, signalling close_event. */
if (user_service->close_pending &&
down_interruptible(&user_service->close_event))
wait_for_completion_interruptible(
&user_service->close_event))
status = VCHIQ_RETRY;
break;
}
Expand Down Expand Up @@ -1182,7 +1185,8 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

DEBUG_TRACE(AWAIT_COMPLETION_LINE);
mutex_unlock(&instance->completion_mutex);
rc = down_interruptible(&instance->insert_event);
rc = wait_for_completion_interruptible(
&instance->insert_event);
mutex_lock(&instance->completion_mutex);
if (rc != 0) {
DEBUG_TRACE(AWAIT_COMPLETION_LINE);
Expand Down Expand Up @@ -1310,7 +1314,7 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
}

if (ret != 0)
up(&instance->remove_event);
complete(&instance->remove_event);
mutex_unlock(&instance->completion_mutex);
DEBUG_TRACE(AWAIT_COMPLETION_LINE);
} break;
Expand Down Expand Up @@ -1350,8 +1354,8 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
do {
spin_unlock(&msg_queue_spinlock);
DEBUG_TRACE(DEQUEUE_MESSAGE_LINE);
if (down_interruptible(
&user_service->insert_event) != 0) {
if (wait_for_completion_interruptible(
&user_service->insert_event)) {
vchiq_log_info(vchiq_arm_log_level,
"DEQUEUE_MESSAGE interrupted");
ret = -EINTR;
Expand All @@ -1373,7 +1377,7 @@ vchiq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
user_service->msg_remove++;
spin_unlock(&msg_queue_spinlock);

up(&user_service->remove_event);
complete(&user_service->remove_event);
if (header == NULL)
ret = -ENOTCONN;
else if (header->size <= args.bufsize) {
Expand Down Expand Up @@ -1979,8 +1983,8 @@ vchiq_open(struct inode *inode, struct file *file)

vchiq_debugfs_add_instance(instance);

sema_init(&instance->insert_event, 0);
sema_init(&instance->remove_event, 0);
init_completion(&instance->insert_event);
init_completion(&instance->remove_event);
mutex_init(&instance->completion_mutex);
mutex_init(&instance->bulk_waiter_list_mutex);
INIT_LIST_HEAD(&instance->bulk_waiter_list);
Expand Down Expand Up @@ -2033,12 +2037,12 @@ vchiq_release(struct inode *inode, struct file *file)

/* Wake the completion thread and ask it to exit */
instance->closing = 1;
up(&instance->insert_event);
complete(&instance->insert_event);

mutex_unlock(&instance->completion_mutex);

/* Wake the slot handler if the completion queue is full. */
up(&instance->remove_event);
complete(&instance->remove_event);

/* Mark all services for termination... */
i = 0;
Expand All @@ -2047,7 +2051,7 @@ vchiq_release(struct inode *inode, struct file *file)
USER_SERVICE_T *user_service = service->base.userdata;

/* Wake the slot handler if the msg queue is full. */
up(&user_service->remove_event);
complete(&user_service->remove_event);

vchiq_terminate_service_internal(service);
unlock_service(service);
Expand All @@ -2059,7 +2063,7 @@ vchiq_release(struct inode *inode, struct file *file)
!= NULL) {
USER_SERVICE_T *user_service = service->base.userdata;

down(&service->remove_event);
wait_for_completion(&service->remove_event);

BUG_ON(service->srvstate != VCHIQ_SRVSTATE_FREE);

Expand Down Expand Up @@ -2103,7 +2107,7 @@ vchiq_release(struct inode *inode, struct file *file)

/* Wake any blocked user-thread */
if (instance->use_close_delivered)
up(&user_service->close_event);
complete(&user_service->close_event);
unlock_service(service);
}
instance->completion_remove++;
Expand Down
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