drm/amd/display: Wait DMCUB to idle state before reset.

[WHY]
Very low rate to cause memory access issue while resetting
DMCUB after the halt command was sent to it.
The process of stopping fw of DMCUB may be timeout, that means
it is not in idle state, such as the window frames may still be
kept in cache, so reset by force will cause MMHUB hang.

[HOW]
After the halt command was sent, keep checking the DMCUB state until
it is idle.

Reviewed-by: Eric Yang <[e-mail]>
Reviewed-by: Nicholas Kazlauskas <[e-mail]>
Acked-by: Jasdeep Dhillon <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: hengzhou <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/inc/hw/dccg.h

···
 	int ref_dppclk;
 	//int dtbclk_khz[MAX_PIPES];/* TODO needs to be removed */
 	//int audio_dtbclk_khz;/* TODO needs to be removed */
-	//int ref_dtbclk_khz;/* TODO needs to be removed */
+	int ref_dtbclk_khz;/* TODO needs to be removed */
 };
 
 struct dtbclk_dto_params {

drivers/gpu/drm/amd/display/dmub/src/dmub_dcn31.c

···
 {
 	union dmub_gpint_data_register cmd;
 	const uint32_t timeout = 100;
-	uint32_t in_reset, scratch, i;
+	uint32_t in_reset, scratch, i, pwait_mode;
 
 	REG_GET(DMCUB_CNTL2, DMCUB_SOFT_RESET, &in_reset);
 
···
 			udelay(1);
 		}
 
+		for (i = 0; i < timeout; ++i) {
+			REG_GET(DMCUB_CNTL, DMCUB_PWAIT_MODE_STATUS, &pwait_mode);
+			if (pwait_mode & (1 << 0))
+				break;
+
+			udelay(1);
+		}
 		/* Force reset in case we timed out, DMCUB is likely hung. */
 	}
 

drivers/gpu/drm/amd/display/dmub/src/dmub_dcn31.h

···
 	DMUB_SF(DCN_VM_FB_OFFSET, FB_OFFSET) \
 	DMUB_SF(DMCUB_INBOX0_WPTR, DMCUB_INBOX0_WPTR) \
 	DMUB_SF(DMCUB_INTERRUPT_ENABLE, DMCUB_GPINT_IH_INT_EN) \
-	DMUB_SF(DMCUB_INTERRUPT_ACK, DMCUB_GPINT_IH_INT_ACK)
+	DMUB_SF(DMCUB_INTERRUPT_ACK, DMCUB_GPINT_IH_INT_ACK) \
+	DMUB_SF(DMCUB_CNTL, DMCUB_PWAIT_MODE_STATUS)
 
 struct dmub_srv_dcn31_reg_offset {
 #define DMUB_SR(reg) uint32_t reg;