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[media] v4l2-dv-timings: fix overflow in gtf timings calculation 

The intermediate calculation in the expression for hblank can exceed
32 bit signed range. This overflow can lead to negative values for
hblank. Typecasting intermediate variable to higher precision.

Cc: Martin Bugge <marbugge@cisco.com>
Signed-off-by: Prashant Laddha <prladdha@cisco.com>
[hans.verkuil@cisco.com: made the denominator u32, since that's what div_u64 expects]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Prashant Laddha 2015-05-05 10:16:27 -03:00 committed by Mauro Carvalho Chehab
parent ed1bc664da
commit c9bc9f5075
1 changed files with 18 additions and 10 deletions
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28
drivers/media/v4l2-core/v4l2-dv-timings.c
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@ -25,6 +25,7 @@
#include <linux/videodev2.h>
#include <linux/v4l2-dv-timings.h>
#include <media/v4l2-dv-timings.h>
#include <linux/math64.h>
MODULE_AUTHOR("Hans Verkuil");
MODULE_DESCRIPTION("V4L2 DV Timings Helper Functions");
@ -554,16 +555,23 @@ bool v4l2_detect_gtf(unsigned frame_height,
image_width = (image_width + GTF_CELL_GRAN/2) & ~(GTF_CELL_GRAN - 1);
/* Horizontal */
if (default_gtf)
h_blank = ((image_width * GTF_D_C_PRIME * hfreq) -
(image_width * GTF_D_M_PRIME * 1000) +
(hfreq * (100 - GTF_D_C_PRIME) + GTF_D_M_PRIME * 1000) / 2) /
(hfreq * (100 - GTF_D_C_PRIME) + GTF_D_M_PRIME * 1000);
else
h_blank = ((image_width * GTF_S_C_PRIME * hfreq) -
(image_width * GTF_S_M_PRIME * 1000) +
(hfreq * (100 - GTF_S_C_PRIME) + GTF_S_M_PRIME * 1000) / 2) /
(hfreq * (100 - GTF_S_C_PRIME) + GTF_S_M_PRIME * 1000);
if (default_gtf) {
u64 num;
u32 den;
num = ((image_width * GTF_D_C_PRIME * (u64)hfreq) -
((u64)image_width * GTF_D_M_PRIME * 1000));
den = hfreq * (100 - GTF_D_C_PRIME) + GTF_D_M_PRIME * 1000;
h_blank = div_u64((num + (den >> 1)), den);
} else {
u64 num;
u32 den;
num = ((image_width * GTF_S_C_PRIME * (u64)hfreq) -
((u64)image_width * GTF_S_M_PRIME * 1000));
den = hfreq * (100 - GTF_S_C_PRIME) + GTF_S_M_PRIME * 1000;
h_blank = div_u64((num + (den >> 1)), den);
}
h_blank = ((h_blank + GTF_CELL_GRAN) / (2 * GTF_CELL_GRAN)) *
(2 * GTF_CELL_GRAN);