media: cec: improve CEC pin event handling

It turns out that the struct cec_fh event buffer size of 64 events
(64 for CEC_EVENT_PIN_CEC_LOW and 64 for _HIGH) is too small. It's
about 160 ms worth of events and if the Raspberry Pi is busy, then it
might take too long for the application to be scheduled so that it can
drain the pending events. Increase these buffers to 800 events which
is at least 2 seconds worth of events.

There is also a FIFO in between the interrupt and the cec-pin thread.
The thread passes the events on to the CEC core. It is important that
should this FIFO fill up the cec core will be informed that events
have been lost so this can be communicated to the user by setting
CEC_EVENT_FL_DROPPED_EVENTS.

It is very hard to debug CEC problems if events were lost without
informing the user of that fact.

If events were dropped due to the FIFO filling up, then the debugfs
status file will let you know how many events were dropped.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/media/cec/cec-pin-priv.h b/drivers/media/cec/cec-pin-priv.h
index dae8ba6f1037..f423db8855d9 100644
--- a/drivers/media/cec/cec-pin-priv.h
+++ b/drivers/media/cec/cec-pin-priv.h
@@ -153,7 +153,9 @@ enum cec_pin_state {
 /* The default for the low/high time of the custom pulse */
 #define CEC_TIM_CUSTOM_DEFAULT				1000
 
-#define CEC_NUM_PIN_EVENTS 128
+#define CEC_NUM_PIN_EVENTS				128
+#define CEC_PIN_EVENT_FL_IS_HIGH			(1 << 0)
+#define CEC_PIN_EVENT_FL_DROPPED			(1 << 1)
 
 #define CEC_PIN_IRQ_UNCHANGED	0
 #define CEC_PIN_IRQ_DISABLE	1
@@ -198,11 +200,13 @@ struct cec_pin {
 	u8				work_tx_status;
 	ktime_t				work_tx_ts;
 	atomic_t			work_irq_change;
-	atomic_t			work_pin_events;
+	atomic_t			work_pin_num_events;
 	unsigned int			work_pin_events_wr;
 	unsigned int			work_pin_events_rd;
 	ktime_t				work_pin_ts[CEC_NUM_PIN_EVENTS];
-	bool				work_pin_is_high[CEC_NUM_PIN_EVENTS];
+	u8				work_pin_events[CEC_NUM_PIN_EVENTS];
+	bool				work_pin_events_dropped;
+	u32				work_pin_events_dropped_cnt;
 	ktime_t				timer_ts;
 	u32				timer_cnt;
 	u32				timer_100ms_overruns;