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path: root/drivers/media/pci/saa7134/saa7134-video.c
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Diffstat (limited to 'drivers/media/pci/saa7134/saa7134-video.c')
-rw-r--r--drivers/media/pci/saa7134/saa7134-video.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/media/pci/saa7134/saa7134-video.c b/drivers/media/pci/saa7134/saa7134-video.c
index 3abf52711e13..7c503fb68526 100644
--- a/drivers/media/pci/saa7134/saa7134-video.c
+++ b/drivers/media/pci/saa7134/saa7134-video.c
@@ -2248,6 +2248,17 @@ static int saa7134_streamon(struct file *file, void *priv,
if (!res_get(dev, fh, res))
return -EBUSY;
+ /* The SAA7134 has a 1K FIFO; the datasheet suggests that when
+ * configured conservatively, there's 22 usec of buffering for video.
+ * We therefore request a DMA latency of 20 usec, giving us 2 usec of
+ * margin in case the FIFO is configured differently to the datasheet.
+ * Unfortunately, I lack register-level documentation to check the
+ * Linux FIFO setup and confirm the perfect value.
+ */
+ pm_qos_add_request(&fh->qos_request,
+ PM_QOS_CPU_DMA_LATENCY,
+ 20);
+
return videobuf_streamon(saa7134_queue(fh));
}
@@ -2259,6 +2270,8 @@ static int saa7134_streamoff(struct file *file, void *priv,
struct saa7134_dev *dev = fh->dev;
int res = saa7134_resource(fh);
+ pm_qos_remove_request(&fh->qos_request);
+
err = videobuf_streamoff(saa7134_queue(fh));
if (err < 0)
return err;