This is a note to let you know that I've just added the patch titled
drm/amd/display: Fix MST PBN/X.Y value calculations
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-amd-display-fix-mst-pbn-x.y-value-calculations.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit d7cf4cb189693982c9e4e448f6f8ff95bd16653e
Author: Ilya Bakoulin <ilya.bakoulin@xxxxxxx>
Date: Fri Dec 1 06:25:06 2023 -0700
drm/amd/display: Fix MST PBN/X.Y value calculations
[ Upstream commit 94bbf802efd0a8f13147d6664af6e653637340a8 ]
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@xxxxxxx>
Reviewed-by: Wenjing Liu <wenjing.liu@xxxxxxx>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@xxxxxxx>
Signed-off-by: Ilya Bakoulin <ilya.bakoulin@xxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpu/drm/amd/display/dc/link/link_dpms.c b/drivers/gpu/drm/amd/display/dc/link/link_dpms.c
index a96f0747628c..b9768cd9b8a0 100644
--- a/drivers/gpu/drm/amd/display/dc/link/link_dpms.c
+++ b/drivers/gpu/drm/amd/display/dc/link/link_dpms.c
@@ -1059,18 +1059,21 @@ 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);
