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drm/radeon: use 64-bit math to calculate CTS values for audio (v2) 

Avoid losing precision.  See bug:
https://bugs.freedesktop.org/show_bug.cgi?id=69675

v2: fix math as per Anssi's comments.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Alex Deucher 2013-09-27 18:09:54 -04:00
parent aaed41ec5b
commit 062c2e4363
1 changed files with 9 additions and 2 deletions
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11
drivers/gpu/drm/radeon/r600_hdmi.c
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@ -75,8 +75,15 @@ static const struct radeon_hdmi_acr r600_hdmi_predefined_acr[] = {
*/
static void r600_hdmi_calc_cts(uint32_t clock, int *CTS, int N, int freq)
{
if (*CTS == 0)
*CTS = clock * N / (128 * freq) * 1000;
u64 n;
u32 d;
if (*CTS == 0) {
n = (u64)clock * (u64)N * 1000ULL;
d = 128 * freq;
do_div(n, d);
*CTS = n;
}
DRM_DEBUG("Using ACR timing N=%d CTS=%d for frequency %d\n",
N, *CTS, freq);
}