[PATCH 13/20] drm/amd/display: disable link before changing link settings

[sunpeng.li at amd.com]

From: Anthony Koo <Anthony.Koo at amd.com>

[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 <Anthony.Koo at amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr at amd.com>
Acked-by: Leo Li <sunpeng.li at amd.com>
Acked-by: Tony Cheng <Tony.Cheng at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 9 +++++++++
 1 file changed, 9 insertions(+)

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 9db5a55..3ef68a2 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);
-- 
2.7.4