[PATCH AUTOSEL 5.4 05/10] drm/amd/display: Prevent bandwidth overflow

Sasha Levin
2020-12-20T03:39:20Z

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 47cefc05fd3f5..f933791f1fbbb 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -2906,11 +2906,14 @@ uint32_t dc_bandwidth_in_kbps_from_timing(
{
uint32_t bits_per_channel = 0;
uint32_t kbps;
+ struct fixed31_32 link_bw_kbps;

#ifdef CONFIG_DRM_AMD_DC_DSC_SUPPORT
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;
}
#endif
--
2.27.0