All,
I think I found a race condition with enabling interrupts in the
streamon call that I wanted some feedback on. I am actually using the
DaVinci PSP 03.03 GA Release (Build 37) kernel but I notice the same issue
in the current linux-davinci kernel that I just pulled down from
git://gitorious.org/linux-davinci/linux-davinci.git. I'll refer to the
latest linux-davinci code in for a discussion of the issue. At the end of
the vpif_streamon there is a call to vb2_streamon() which then invokes
vpif_start_streaming. At the end of vpif_start_streaming() the
channel_first_int[][] variable is set to 1 as a flag the ISR that the next
time it runs. However this line of code follows the code that enables the
interrupt. I was getting a race where the interrupt was enabled in
streamon(), then the ISR ran prior to the channel_first_int getting set.
This ended up hanging my user code in a Capture_get call. The problem crops
up randomly but frequently enough that it wasn't viable.
I have just started looking into the vpif kernel code recently to
find out why my video input was hanging so I am not familiar with much of
the vpif cod, but it kind of made sense to reset the channel_first_int flag
that the interrupt handler queries prior to enabling the interrupts. I
moved that setting of the flag prior to setting the interrupts and it fixed
my issue. I made this change on my DaVinci PSP 03.03 GA Release (Build 37),
but look forward to testing with the freshest linux-davinci kernel.
Unfortunately it'll take some time to get my custom drivers for my video
chips ported over to that kernel.
Here's the diff:
diff --git a/drivers/media/video/davinci/vpif_capture.c
b/drivers/media/video/davinci/vpif_capture.c
index 266025e..2e13d8b 100644
--- a/drivers/media/video/davinci/vpif_capture.c
+++ b/drivers/media/video/davinci/vpif_capture.c
@@ -337,8 +337,10 @@ static int vpif_start_streaming(struct vb2_queue *vq,
unsigned int count)
/**
* Set interrupt for both the fields in VPIF Register enable channel
in
- * VPIF register
+ * VPIF register. First set the channel_first_int flag for the
interrupt
+ * handler to pickup when it is asserted.
*/
+ channel_first_int[VPIF_VIDEO_INDEX][ch->channel_id] = 1;
if ((VPIF_CHANNEL0_VIDEO == ch->channel_id)) {
channel0_intr_assert();
channel0_intr_enable(1);
@@ -350,7 +352,6 @@ static int vpif_start_streaming(struct vb2_queue *vq,
unsigned int count)
channel1_intr_enable(1);
enable_channel1(1);
}
- channel_first_int[VPIF_VIDEO_INDEX][ch->channel_id] = 1;
return 0;
}
---
David Oleszkiewicz
Adsys Controls, Inc.
949-436-4848
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