drm/amd/display: Fix takover from VGA mode

[linux.git] / drivers / gpu / drm / amd / display / dc / dcn10 / dcn10_hw_sequencer.c

diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
index 7b959fa2351ef7ce809768ea0ed843fad30056fd..f07a8a3d5c25993168d9117c096d9fdf3b06110b 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
@@ -242,6 +242,16 @@ static void disable_vga(
        REG_WRITE(D2VGA_CONTROL, 0);
        REG_WRITE(D3VGA_CONTROL, 0);
        REG_WRITE(D4VGA_CONTROL, 0);
+
+       /* HW Engineer's Notes:
+        *  During switch from vga->extended, if we set the VGA_TEST_ENABLE and
+        *  then hit the VGA_TEST_RENDER_START, then the DCHUBP timing gets updated correctly.
+        *
+        *  Then vBIOS will have it poll for the VGA_TEST_RENDER_DONE and unset
+        *  VGA_TEST_ENABLE, to leave it in the same state as before.
+        */
+       REG_UPDATE(VGA_TEST_CONTROL, VGA_TEST_ENABLE, 1);
+       REG_UPDATE(VGA_TEST_CONTROL, VGA_TEST_RENDER_START, 1);
 }
 
 static void dpp_pg_control(