drm/amd/display: Fix takover from VGA mode

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.

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dce_hwseq.h

@@ -236,6 +236,7 @@
 	SR(D2VGA_CONTROL), \
 	SR(D3VGA_CONTROL), \
 	SR(D4VGA_CONTROL), \
+	SR(VGA_TEST_CONTROL), \
 	SR(DC_IP_REQUEST_CNTL), \
 	BL_REG_LIST()
 
@@ -337,6 +338,7 @@ struct dce_hwseq_registers {
 	uint32_t D2VGA_CONTROL;
 	uint32_t D3VGA_CONTROL;
 	uint32_t D4VGA_CONTROL;
+	uint32_t VGA_TEST_CONTROL;
 	/* MMHUB registers. read only. temporary hack */
 	uint32_t VM_CONTEXT0_PAGE_TABLE_BASE_ADDR_HI32;
 	uint32_t VM_CONTEXT0_PAGE_TABLE_BASE_ADDR_LO32;
@@ -494,7 +496,9 @@ struct dce_hwseq_registers {
 	HWS_SF(, DOMAIN7_PG_STATUS, DOMAIN7_PGFSM_PWR_STATUS, mask_sh), \
 	HWS_SF(, DC_IP_REQUEST_CNTL, IP_REQUEST_EN, mask_sh), \
 	HWS_SF(, LVTMA_PWRSEQ_CNTL, LVTMA_BLON, mask_sh), \
-	HWS_SF(, LVTMA_PWRSEQ_STATE, LVTMA_PWRSEQ_TARGET_STATE_R, mask_sh)
+	HWS_SF(, LVTMA_PWRSEQ_STATE, LVTMA_PWRSEQ_TARGET_STATE_R, mask_sh), \
+	HWS_SF(, VGA_TEST_CONTROL, VGA_TEST_ENABLE, mask_sh),\
+	HWS_SF(, VGA_TEST_CONTROL, VGA_TEST_RENDER_START, mask_sh)
 
 #define HWSEQ_REG_FIELD_LIST(type) \
 	type DCFE_CLOCK_ENABLE; \
@@ -583,7 +587,9 @@ struct dce_hwseq_registers {
 	type DCFCLK_GATE_DIS; \
 	type DCHUBBUB_GLOBAL_TIMER_REFDIV; \
 	type DENTIST_DPPCLK_WDIVIDER; \
-	type DENTIST_DISPCLK_WDIVIDER;
+	type DENTIST_DISPCLK_WDIVIDER; \
+	type VGA_TEST_ENABLE; \
+	type VGA_TEST_RENDER_START;
 
 struct dce_hwseq_shift {
 	HWSEQ_REG_FIELD_LIST(uint8_t)

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(