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;