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Subject[PATCH 5/5] staging/easycap: Fix bytesperline calculation
Date
As described above fillin_formats()

"""
/*
* THE 16-BIT easycap_format.mask HAS MEANING:
* (least significant) BIT 0: 0 => PAL, 25 FPS; 1 => NTSC, 30 FPS
* BITS 2-4: RESERVED FOR DIFFERENTIATING STANDARDS
* BITS 5-7: NUMBER OF BYTES PER PIXEL
* BIT 8: 0 => NATIVE BYTE ORDER; 1 => SWAPPED
* BITS 9-10: RESERVED FOR OTHER BYTE PERMUTATIONS
* BIT 11: 0 => UNDECIMATED; 1 => DECIMATED
* BIT 12: 0 => OFFER FRAMES; 1 => OFFER FIELDS
* BIT 13: 0 => FULL FRAMERATE; 1 => REDUCED
* (most significant) BITS 14-15: RESERVED FOR OTHER FIELD/FRAME OPTIONS
* IT FOLLOWS THAT:
* bytesperpixel IS ((0x00E0 & easycap_format.mask) >> 5)
* byteswaporder IS true IF (0 != (0x0100 & easycap_format.mask))
*
* decimatepixel IS true IF (0 != (0x0800 & easycap_format.mask))
*
* offerfields IS true IF (0 != (0x1000 & easycap_format.mask))
*/
"""
bytes-per-pixel is stored in bits 5-7 of calculated mask.

But when calculating bytes-per-line we were extracting wrong value
instead of bytes-per-pixel, which was usually 2 times bigger -- e.g. for
PAL YUV 422 I was getting ((mask3 & 0x00F0) >> 4) = 4 bytes instead of 2.

The error here is that even in comments there is a line saying

* bytesperpixel IS ((0x00E0 & easycap_format.mask) >> 5)

but we were using
((0x00F0 & easycap_format.mask) >> 4)

With 2 times bigger bytesperpixel and automatically bytesperline, the
video was shown halfheight'ed, which is understandable if we look at
video-memory layout:

<------- bytesperline -------->
<- real bpl ->
x0----------y0 x1-----------y1
x2----------y2 x3-----------y3
xn----------yn xn-----------yn
<garbage>
for each line, we should display width pixels, then move to next line
with bytesperline, and oops, if bytesperline = 2*real-bytesperlin, we'll
skip one line and move to next-next line, and so only half lines will be
shown.

Initially I've debugged the problem with my video application[1], but
I've checked that after this patch both rawv (mine app) and tvtime work
correctly.

[1] http://repo.or.cz/w/rawv.git

P.S. why at all we use those mask/shifts? Why not use bitfields?

Cc: Tomas Winkler <tomas.winkler@intel.com>
Cc: Mike Thomas <rmthomas@sciolus.org>
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
---
drivers/staging/easycap/easycap_settings.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/staging/easycap/easycap_settings.c b/drivers/staging/easycap/easycap_settings.c
index 898559d..70f59b1 100644
--- a/drivers/staging/easycap/easycap_settings.c
+++ b/drivers/staging/easycap/easycap_settings.c
@@ -567,7 +567,7 @@ int fillin_formats(void)
default:
return -3;
}
- bytesperline = width * ((mask3 & 0x00F0) >> 4);
+ bytesperline = width * ((mask3 & 0x00E0) >> 5);
sizeimage = bytesperline * height;

for (m = 0; m < INTERLACE_MANY; m++) {
--
1.7.6.rc1


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