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drm/amd/display: Fix MST PBN/X.Y value calculations

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Changing PBN calculation to be more in line with spec. We don't need to
inflate PBN_NATIVE value by the 1.006 margin, since that is already
taken care of in the get_pbn_per_slot function.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Ilya Bakoulin <ilya.bakoulin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Ilya Bakoulin
2023-12-01 06:25:06 -07:00
committed by Alex Deucher
parent 23cf5a5cd3
commit 94bbf802ef
1 changed files with 8 additions and 5 deletions
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drivers/gpu/drm/amd/display/dc/link/link_dpms.c
+8 -5
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@@ -1057,18 +1057,21 @@ static struct fixed31_32 get_pbn_from_bw_in_kbps(uint64_t kbps)
uint32_t denominator = 1;
/*
* margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
* The 1.006 factor (margin 5300ppm + 300ppm ~ 0.6% as per spec) is not
* required when determining PBN/time slot utilization on the link between
* us and the branch, since that overhead is already accounted for in
* the get_pbn_per_slot function.
*
* 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
* peak_kbps /= (8 * 1000) convert to bytes
*/
numerator = 64 * PEAK_FACTOR_X1000;
denominator = 54 * 8 * 1000 * 1000;
numerator = 64;
denominator = 54 * 8 * 1000;
kbps *= numerator;
peak_kbps = dc_fixpt_from_fraction(kbps, denominator);