[PATCH 1/2]: media: hdpvr: Add adaptive sleeping in hdpvr_start_streaming

[Keith Pyle <kpyle@austin.rr.com>]

The hdpvr firmware reacts poorly to a fast close/open sequence.  Delaying
a few seconds between the close and next open produces generally reliable
results.  Rather than requiring user programs to implement this delay and
coordinate among themselves when the device is handed from one program to
another, add kernel support for delaying the attempt to start streaming if
the device only recently stopped streaming.  A delay of 4 seconds seems to
be sufficient, but some administrators may wish to push their luck by
trying shorter delays.  To allow administrators to change the delay, add a
new parameter to the hdpvr module: `hdpvr_close_to_open_ms_delay`, which
specifies the delay in milliseconds between a close and subsequent
start-streaming.  If the user application has already delayed by at least
that long for its own reasons, this feature will add no further delay.

Signed-off-by: Keith Pyle <kpyle@austin.rr.com>
Tested-by: Keith Pyle <kpyle@austin.rr.com>
---
Changes since v1:
- Rewrapped output at 80 columns, per request from Hans.  Literal strings
still exceed 80 columns where necessary to keep an entire string together,
since this makes it easier for grep to find the file and line that
generates a given message.
- Reviewed Hans request to use `jiffies` instead of `get_jiffies_64()`.
Per the documentation, raw `jiffies` appears to be inappropriate
on 32-bit systems, so the patch continues to use `get_jiffies_64()`.
On 64-bit systems, `get_jiffies_64()` becomes a direct read of `jiffies`.
Further, both uses of `get_jiffies_64()` are on relatively cold paths
(one just before starting streaming, the other just before a 10ms
hardcoded sleep), so the performance impact even on the 32-bit path
should be trivial relative to the time required for the surrounding code.
---
 drivers/media/usb/hdpvr/hdpvr-core.c  |  4 ++++
 drivers/media/usb/hdpvr/hdpvr-video.c | 22 ++++++++++++++++++++++
 drivers/media/usb/hdpvr/hdpvr.h       |  5 +++++
 3 files changed, 31 insertions(+)

diff --git a/drivers/media/usb/hdpvr/hdpvr-core.c b/drivers/media/usb/hdpvr/hdpvr-core.c
index 23d3d0754308..fd7608e7e94c 100644
--- a/drivers/media/usb/hdpvr/hdpvr-core.c
+++ b/drivers/media/usb/hdpvr/hdpvr-core.c
@@ -39,6 +39,10 @@ int hdpvr_debug;
 module_param(hdpvr_debug, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(hdpvr_debug, "enable debugging output");
 
+uint hdpvr_close_to_open_ms_delay = 4000;
+module_param(hdpvr_close_to_open_ms_delay, uint, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(hdpvr_close_to_open_ms_delay, "delay restarting streaming by the specified number of milliseconds");
+
 static uint default_video_input = HDPVR_VIDEO_INPUTS;
 module_param(default_video_input, uint, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(default_video_input, "default video input: 0=Component / 1=S-Video / 2=Composite");
diff --git a/drivers/media/usb/hdpvr/hdpvr-video.c b/drivers/media/usb/hdpvr/hdpvr-video.c
index 3d199d5d6738..8a2b883d372e 100644
--- a/drivers/media/usb/hdpvr/hdpvr-video.c
+++ b/drivers/media/usb/hdpvr/hdpvr-video.c
@@ -278,6 +278,8 @@ static int hdpvr_start_streaming(struct hdpvr_device *dev)
 {
 	int ret;
 	struct hdpvr_video_info vidinf;
+	u64 now_jiffies, delta_jiffies;
+	uint msec_to_sleep;
 
 	if (dev->status == STATUS_STREAMING)
 		return 0;
@@ -298,6 +300,22 @@ static int hdpvr_start_streaming(struct hdpvr_device *dev)
 	v4l2_dbg(MSG_BUFFER, hdpvr_debug, &dev->v4l2_dev,
 			"video signal: %dx%d@%dhz\n", vidinf.width,
 			vidinf.height, vidinf.fps);
+	now_jiffies = get_jiffies_64();
+	/* inline time_after64 since the result of the subtraction is needed
+	 * for the sleep
+	 */
+	delta_jiffies = dev->jiffies_next_start_streaming - now_jiffies;
+	if ((__s64)delta_jiffies > 0) {
+		/* device firmware may not be ready yet */
+		msec_to_sleep = jiffies_to_msecs(delta_jiffies);
+		v4l2_dbg(MSG_INFO, hdpvr_debug, &dev->v4l2_dev,
+			 "firmware may not be ready, sleeping for %u ms\n",
+			 msec_to_sleep);
+		msleep(msec_to_sleep);
+	} else {
+		v4l2_dbg(MSG_INFO, hdpvr_debug, &dev->v4l2_dev,
+			 "firmware assumed to be ready, not sleeping\n");
+	}
 
 	/* start streaming 2 request */
 	hdpvr_usb_lock(dev, HDPVR_USB_CTRL);
@@ -332,6 +350,7 @@ static int hdpvr_stop_streaming(struct hdpvr_device *dev)
 	int actual_length;
 	uint c = 0;
 	u8 *buf;
+	u64 now_jiffies;
 
 	if (dev->status == STATUS_IDLE)
 		return 0;
@@ -368,6 +387,9 @@ static int hdpvr_stop_streaming(struct hdpvr_device *dev)
 	kfree(buf);
 	v4l2_dbg(MSG_BUFFER, hdpvr_debug, &dev->v4l2_dev,
 		 "used %d urbs to empty device buffers\n", c-1);
+	now_jiffies = get_jiffies_64();
+	dev->jiffies_next_start_streaming = now_jiffies +
+		msecs_to_jiffies(hdpvr_close_to_open_ms_delay);
 	msleep(10);
 
 	dev->status = STATUS_IDLE;
diff --git a/drivers/media/usb/hdpvr/hdpvr.h b/drivers/media/usb/hdpvr/hdpvr.h
index 7b3d166da1dd..9e5f88146827 100644
--- a/drivers/media/usb/hdpvr/hdpvr.h
+++ b/drivers/media/usb/hdpvr/hdpvr.h
@@ -43,6 +43,7 @@
 /* #define HDPVR_DEBUG */
 
 extern int hdpvr_debug;
+extern uint hdpvr_close_to_open_ms_delay;
 
 #define MSG_INFO	1
 #define MSG_BUFFER	2
@@ -95,6 +96,10 @@ struct hdpvr_device {
 	struct v4l2_dv_timings	cur_dv_timings;
 
 	uint			flags;
+	/* earliest jiffies at which the device firmware will be ready to
+	 * start streaming
+	 */
+	u64             jiffies_next_start_streaming;
 
 	/* synchronize I/O */
 	struct mutex		io_mutex;
-- 
2.22.0