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drm/dp/mst: Calculate MST PBN with 31.32 fixed point

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Our PBN value overflows the 20 bits integer part of the 20.12
fixed point. We need to use 31.32 fixed point to avoid this.

This happens with display clocks larger than 293122 (at 24 bpp),
which we see with the Sharp (and similar) 4k tiled displays.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Harry Wentland 2016-01-22 17:07:26 -05:00 committed by Dave Airlie
parent 64566b5e76
commit a9ebb3e46c
1 changed files with 35 additions and 24 deletions
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59
drivers/gpu/drm/drm_dp_mst_topology.c
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@ -2606,32 +2606,31 @@ EXPORT_SYMBOL(drm_dp_check_act_status);
*/
int drm_dp_calc_pbn_mode(int clock, int bpp)
{
fixed20_12 pix_bw;
fixed20_12 fbpp;
fixed20_12 result;
fixed20_12 margin, tmp;
u32 res;
u64 kbps;
s64 peak_kbps;
u32 numerator;
u32 denominator;
pix_bw.full = dfixed_const(clock);
fbpp.full = dfixed_const(bpp);
tmp.full = dfixed_const(8);
fbpp.full = dfixed_div(fbpp, tmp);
kbps = clock * bpp;
result.full = dfixed_mul(pix_bw, fbpp);
margin.full = dfixed_const(54);
tmp.full = dfixed_const(64);
margin.full = dfixed_div(margin, tmp);
result.full = dfixed_div(result, margin);
/*
* margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
* The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
* common multiplier to render an integer PBN for all link rate/lane
* counts combinations
* calculate
* peak_kbps *= (1006/1000)
* peak_kbps *= (64/54)
* peak_kbps *= 8 convert to bytes
*/
margin.full = dfixed_const(1006);
tmp.full = dfixed_const(1000);
margin.full = dfixed_div(margin, tmp);
result.full = dfixed_mul(result, margin);
numerator = 64 * 1006;
denominator = 54 * 8 * 1000 * 1000;
result.full = dfixed_div(result, tmp);
result.full = dfixed_ceil(result);
res = dfixed_trunc(result);
return res;
kbps *= numerator;
peak_kbps = drm_fixp_from_fraction(kbps, denominator);
return drm_fixp2int_ceil(peak_kbps);
}
EXPORT_SYMBOL(drm_dp_calc_pbn_mode);
@ -2639,11 +2638,23 @@ static int test_calc_pbn_mode(void)
{
int ret;
ret = drm_dp_calc_pbn_mode(154000, 30);
if (ret != 689)
if (ret != 689) {
DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
154000, 30, 689, ret);
return -EINVAL;
}
ret = drm_dp_calc_pbn_mode(234000, 30);
if (ret != 1047)
if (ret != 1047) {
DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
234000, 30, 1047, ret);
return -EINVAL;
}
ret = drm_dp_calc_pbn_mode(297000, 24);
if (ret != 1063) {
DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
297000, 24, 1063, ret);
return -EINVAL;
}
return 0;
}