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[media] rc: refactor raw handler kthread

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I think we can get rid of the spinlock protecting the kthread from being
interrupted by a wakeup in certain parts.
Even with the current implementation of the kthread the only lost wakeup
scenario could happen if the wakeup occurs between the kfifo_len check
and setting the state to TASK_INTERRUPTIBLE.

In the changed version we could lose a wakeup if it occurs between
processing the fifo content and setting the state to TASK_INTERRUPTIBLE.
This scenario is covered by an additional check for available events in
the fifo and setting the state to TASK_RUNNING in this case.

In addition the changed version flushes the kfifo before ending
when the kthread is stopped.

With this patch we gain:
- Get rid of the spinlock
- Simplify code
- Don't grep / release the mutex for each individual event but just once
  for the complete fifo content. This reduces overhead if a driver e.g.
  triggers processing after writing the content of a hw fifo to the kfifo.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Heiner Kallweit 2016-08-02 02:44:07 -03:00 committed by Mauro Carvalho Chehab
parent 0cffd6312f
commit 74d47d75be
2 changed files with 18 additions and 32 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
drivers/media/rc/rc-core-priv.h
View file

@ -20,7 +20,6 @@
#define MAX_IR_EVENT_SIZE 512
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <media/rc-core.h>
struct ir_raw_handler {
@ -37,7 +36,6 @@ struct ir_raw_handler {
struct ir_raw_event_ctrl {
struct list_head list; /* to keep track of raw clients */
struct task_struct *thread;
spinlock_t lock;
/* fifo for the pulse/space durations */
DECLARE_KFIFO(kfifo, struct ir_raw_event, MAX_IR_EVENT_SIZE);
ktime_t last_event; /* when last event occurred */

48
drivers/media/rc/rc-ir-raw.c
View file

@ -17,7 +17,6 @@
#include <linux/mutex.h>
#include <linux/kmod.h>
#include <linux/sched.h>
#include <linux/freezer.h>
#include "rc-core-priv.h"
/* Used to keep track of IR raw clients, protected by ir_raw_handler_lock */
@ -34,32 +33,26 @@ static int ir_raw_event_thread(void *data)
struct ir_raw_handler *handler;
struct ir_raw_event_ctrl *raw = (struct ir_raw_event_ctrl *)data;
while (!kthread_should_stop()) {
spin_lock_irq(&raw->lock);
if (!kfifo_len(&raw->kfifo)) {
set_current_state(TASK_INTERRUPTIBLE);
if (kthread_should_stop())
set_current_state(TASK_RUNNING);
spin_unlock_irq(&raw->lock);
schedule();
continue;
}
if(!kfifo_out(&raw->kfifo, &ev, 1))
dev_err(&raw->dev->dev, "IR event FIFO is empty!\n");
spin_unlock_irq(&raw->lock);
while (1) {
mutex_lock(&ir_raw_handler_lock);
list_for_each_entry(handler, &ir_raw_handler_list, list)
if (raw->dev->enabled_protocols & handler->protocols ||
!handler->protocols)
handler->decode(raw->dev, ev);
raw->prev_ev = ev;
while (kfifo_out(&raw->kfifo, &ev, 1)) {
list_for_each_entry(handler, &ir_raw_handler_list, list)
if (raw->dev->enabled_protocols &
handler->protocols || !handler->protocols)
handler->decode(raw->dev, ev);
raw->prev_ev = ev;
}
mutex_unlock(&ir_raw_handler_lock);
set_current_state(TASK_INTERRUPTIBLE);
if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
break;
} else if (!kfifo_is_empty(&raw->kfifo))
set_current_state(TASK_RUNNING);
schedule();
}
return 0;
@ -218,14 +211,10 @@ EXPORT_SYMBOL_GPL(ir_raw_event_set_idle);
*/
void ir_raw_event_handle(struct rc_dev *dev)
{
unsigned long flags;
if (!dev->raw)
return;
spin_lock_irqsave(&dev->raw->lock, flags);
wake_up_process(dev->raw->thread);
spin_unlock_irqrestore(&dev->raw->lock, flags);
}
EXPORT_SYMBOL_GPL(ir_raw_event_handle);
@ -269,7 +258,6 @@ int ir_raw_event_register(struct rc_dev *dev)
dev->change_protocol = change_protocol;
INIT_KFIFO(dev->raw->kfifo);
spin_lock_init(&dev->raw->lock);
dev->raw->thread = kthread_run(ir_raw_event_thread, dev->raw,
"rc%u", dev->minor);