From: Chris Park Chris.Park@amd.com

[ Upstream commit 80089dd8410f356d5104496d5ab71a66a4f4646b ]

[Why] At very high pixel clock, bandwidth calculation exceeds 32 bit size and overflow value. This causes the resulting selection of link rate to be inaccurate.

[How] Change order of operation and use fixed point to deal with integer accuracy. Also address bug found when forcing link rate.

Signed-off-by: Chris Park Chris.Park@amd.com Reviewed-by: Wenjing Liu Wenjing.Liu@amd.com Acked-by: Eryk Brol eryk.brol@amd.com Signed-off-by: Alex Deucher alexander.deucher@amd.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/amd/display/dc/core/dc_link.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c index b0f8bfd48d102..462f8b18440b3 100644 --- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c +++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c @@ -3394,10 +3394,13 @@ uint32_t dc_bandwidth_in_kbps_from_timing( { uint32_t bits_per_channel = 0; uint32_t kbps; + struct fixed31_32 link_bw_kbps;

if (timing->flags.DSC) { - kbps = (timing->pix_clk_100hz * timing->dsc_cfg.bits_per_pixel); - kbps = kbps / 160 + ((kbps % 160) ? 1 : 0); + link_bw_kbps = dc_fixpt_from_int(timing->pix_clk_100hz); + link_bw_kbps = dc_fixpt_div_int(link_bw_kbps, 160); + link_bw_kbps = dc_fixpt_mul_int(link_bw_kbps, timing->dsc_cfg.bits_per_pixel); + kbps = dc_fixpt_ceil(link_bw_kbps); return kbps; }