[PATCH 5.4 044/152] drm/amd/display: Limit minimum DPPCLK to 100MHz.

Greg Kroah-Hartman
2020-03-03T17:54:02Z

From: Yongqiang Sun <yongqiang.sun@amd.com>

[ Upstream commit 6c81917a0485ee2a1be0dc23321ac10ecfd9578b ]

[Why]
Underflow is observed when plug in a 4K@60 monitor with
1366x768 eDP due to DPPCLK is too low.

[How]
Limit minimum DPPCLK to 100MHz.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@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/clk_mgr/dcn21/rn_clk_mgr.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c
index 787f94d815f42..dd92f9c295b45 100644
--- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c
+++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c
@@ -91,6 +91,12 @@ void rn_update_clocks(struct clk_mgr *clk_mgr_base,
rn_vbios_smu_set_min_deep_sleep_dcfclk(clk_mgr, clk_mgr_base->clks.dcfclk_deep_sleep_khz);
}

+ // workaround: Limit dppclk to 100Mhz to avoid lower eDP panel switch to plus 4K monitor underflow.
+ if (!IS_DIAG_DC(dc->ctx->dce_environment)) {
+ if (new_clocks->dppclk_khz < 100000)
+ new_clocks->dppclk_khz = 100000;
+ }
+
if (should_set_clock(safe_to_lower, new_clocks->dppclk_khz, clk_mgr->base.clks.dppclk_khz)) {
if (clk_mgr->base.clks.dppclk_khz > new_clocks->dppclk_khz)
dpp_clock_lowered = true;
--
2.20.1