[PATCH 3.10 164/173] drm/radeon: use 64-bit math to calculate CTS values for audio (v2)

Greg Kroah-Hartman
2013-12-02T19:12:27Z

From: Alex Deucher <alexander.deucher@amd.com>

commit 062c2e4363451d49ef840232fe65e8bff0dde2a5 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/radeon/r600_hdmi.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/radeon/r600_hdmi.c
+++ b/drivers/gpu/drm/radeon/r600_hdmi.c
@@ -75,8 +75,15 @@ static const struct radeon_hdmi_acr r600
*/
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);
}