[media] saa7134: Add pm_qos_request to fix video corruption

The SAA7134 appears to have trouble buffering more than one line of video
when doing DMA. Rather than try to fix the driver to cope (as has been done
by Andy Walls for the cx18 driver), put in a pm_qos_request to limit deep
sleep exit latencies.
The visible effect of not having this is that seemingly random lines are
only partly transferred - if you feed in a static image, you see a portion
of the image "flicker" into place.

[mchehab@redhat.com: Fix ABI breakage due to some renames at pm_qos]
Signed-off-by: Simon Farnsworth <simon.farnsworth@onelan.co.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

2 files changed, 15 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;
diff --git a/drivers/media/pci/saa7134/saa7134.h b/drivers/media/pci/saa7134/saa7134.h
index c24b6512bd8f..0a3feaa8589b 100644
--- a/drivers/media/pci/saa7134/saa7134.h
+++ b/drivers/media/pci/saa7134/saa7134.h
@@ -29,6 +29,7 @@
 #include <linux/notifier.h>
 #include <linux/delay.h>
 #include <linux/mutex.h>
+#include <linux/pm_qos.h>
 
 #include <asm/io.h>
 
@@ -469,6 +470,7 @@ struct saa7134_fh {
         enum v4l2_buf_type         type;
         unsigned int               resources;
         enum v4l2_priority         prio;
+        struct pm_qos_request      qos_request;
 
         /* video overlay */
         struct v4l2_window         win;