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[media] tvp5150: COMPOSITE0 input should not force-enable TV mode

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When digitizing composite video from a analog videotape source using the
TVP5150's first composite input channel, the captured stream exhibits
tearing and synchronization problems[1].

It turns out that commit c0477ad9fe caused
"TV mode" (as opposed to "VCR mode" or "auto-detect") to be forcibly
enabled for both composite inputs.  According to the chip
documentation[2], "TV mode" disables a "chrominance trap" input filter,
which appears to be necessary for high-quality video capture from an
analog videotape source.  [ Commit
c7c0b34c27 subsequently restricted the
problem to the first composite input, apparently inadvertently. ]

Since any type of composite signal source can be connected to the
TVP5150's first composite input, unconditionally forcing "TV mode" isn't
correct.  There doesn't appear to be a good way for applications to tell
the driver what is connected.  Fortunately, the TVP5150 has an operating
mode auto-detection feature, which, when enabled, should cause the TVP5150
to auto-detect whether it should use "VCR mode" or "TV mode".  Enabling
operating mode auto-detection improved video capture quality
significantly[3].

Therefore, fix this bug by using operating mode auto-detection. (Also,
while here, fix a CodingStyle issue.)

For those users who may find this patch via a mailing list archive but who
are not able to upgrade to a kernel with a fixed driver: the TVP5150's
S-Video and second composite input sources have auto-detection enabled, so
you may wish to try using those -- if available on your device -- until
this fix makes it a downstream distribution near you.

1. Pre-patch tvtime snapshot using a Pinnacle PCTV HD Pro as the
   capture device and a Sony EV-S2000 as a video source:
   http://www.booyaka.com/~paul/tvp5150/1a.png

2. Section 3.21.3, "Operation Mode Control Register", _TVP5150AM1
   Ultralow-Power NTSC/PAL/SECAM Video Decoder (Rev. D)_ [SLES209D],
   downloaded 8 October 2010, available via
   http://focus.ti.com/lit/ds/symlink/tvp5150am1.pdf

3. Post-patch tvtime snapshot (same signal chain as #1, above):
   http://www.booyaka.com/~paul/tvp5150/1b.png

Signed-off-by: Paul Walmsley <paul@booyaka.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Paul Walmsley 2010-10-09 01:31:40 -03:00 committed by Mauro Carvalho Chehab
parent a06423c9a2
commit 2962fc0120
1 changed files with 1 additions and 3 deletions
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4
drivers/media/video/tvp5150.c
View file

@ -276,7 +276,7 @@ static int tvp5150_log_status(struct v4l2_subdev *sd)
static inline void tvp5150_selmux(struct v4l2_subdev *sd)
{
int opmode=0;
int opmode = 0;
struct tvp5150 *decoder = to_tvp5150(sd);
int input = 0;
unsigned char val;
@ -289,12 +289,10 @@ static inline void tvp5150_selmux(struct v4l2_subdev *sd)
input |= 2;
/* fall through */
case TVP5150_COMPOSITE0:
opmode=0x30; /* TV Mode */
break;
case TVP5150_SVIDEO:
default:
input |= 1;
opmode=0; /* Auto Mode */
break;
}