drm/amd/display: FEC check in timing validation

stable inclusion
from stable-v5.10.112
commit 6906e05cf3ad2cfe704eda003de59aa0cb89b291
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5HL0X

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6906e05cf3ad2cfe704eda003de59aa0cb89b291

--------------------------------

[ Upstream commit 7d56a154 ]

[Why]
disable/enable leads FEC mismatch between hw/sw FEC state.

[How]
check FEC status to fastboot on/off.
Reviewed-by: NAnthony Koo <Anthony.Koo@amd.com>
Acked-by: NAlex Hung <alex.hung@amd.com>
Signed-off-by: NChiawen Huang <chiawen.huang@amd.com>
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -1173,6 +1173,10 @@ bool dc_validate_seamless_boot_timing(const struct dc *dc,
 	if (!link->link_enc->funcs->is_dig_enabled(link->link_enc))
 		return false;
 
+	/* Check for FEC status*/
+	if (link->link_enc->funcs->fec_is_active(link->link_enc))
+		return false;
+
 	enc_inst = link->link_enc->funcs->get_dig_frontend(link->link_enc);
 
 	if (enc_inst == ENGINE_ID_UNKNOWN)