drm/amd/display: disable link before changing link settings

[Why]
If link is already enabled at a different rate (for example 5.4 Gbps)
then calling VBIOS command table to switch to a new rate
(for example 2.7 Gbps) will not take effect.
This can lead to link training failure to occur.

[How]
If the requested link rate is different than the current link rate,
the link must be disabled in order to re-enable at the new
link rate.

In today's logic it is currently only impacting eDP since DP
connection types will always disable the link during display
detection, when initial link verification occurs.

Signed-off-by: Anthony Koo <[email protected]>
Reviewed-by: Aric Cyr <[email protected]>
Acked-by: Leo Li <[email protected]>
Acked-by: Tony Cheng <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

1 files changed, 9 insertions, 0 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 c0d1d83ae4c5..3b1e38e110ee 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -1396,6 +1396,15 @@ static enum dc_status enable_link_dp(
 	/* get link settings for video mode timing */
 	decide_link_settings(stream, &link_settings);
 
+	/* If link settings are different than current and link already enabled
+	 * then need to disable before programming to new rate.
+	 */
+	if (link->link_status.link_active &&
+		(link->cur_link_settings.lane_count != link_settings.lane_count ||
+		 link->cur_link_settings.link_rate != link_settings.link_rate)) {
+		dp_disable_link_phy(link, pipe_ctx->stream->signal);
+	}
+
 	pipe_ctx->stream_res.pix_clk_params.requested_sym_clk =
 			link_settings.link_rate * LINK_RATE_REF_FREQ_IN_KHZ;
 	state->clk_mgr->funcs->update_clocks(state->clk_mgr, state, false);