drm/amd/display: Apply 60us prefetch for DCFCLK <= 300Mhz

[Description]
- Previously we wanted to apply extra 60us of prefetch for min DCFCLK
(200Mhz), but DCFCLK can be calculated to be 201Mhz which underflows
also without the extra prefetch
- Instead, apply the the extra 60us prefetch for any DCFCLK freq <=
300Mhz

Reviewed-by: Nevenko Stupar <[e-mail]>
Reviewed-by: Jun Lei <[e-mail]>
Acked-by: Tom Chung <[e-mail]>
Signed-off-by: Alvin Lee <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c

···
 					v->SwathHeightC[k],
 					TWait,
 					(v->DRAMSpeedPerState[mode_lib->vba.VoltageLevel] <= MEM_STROBE_FREQ_MHZ ||
-						v->DCFCLKPerState[mode_lib->vba.VoltageLevel] <= MIN_DCFCLK_FREQ_MHZ) ?
+						v->DCFCLKPerState[mode_lib->vba.VoltageLevel] <= DCFCLK_FREQ_EXTRA_PREFETCH_REQ_MHZ) ?
 							mode_lib->vba.ip.min_prefetch_in_strobe_us : 0,
 					/* Output */
 					&v->DSTXAfterScaler[k],
···
 							v->swath_width_chroma_ub_this_state[k],
 							v->SwathHeightYThisState[k],
 							v->SwathHeightCThisState[k], v->TWait,
-							(v->DRAMSpeedPerState[i] <= MEM_STROBE_FREQ_MHZ || v->DCFCLKState[i][j] <= MIN_DCFCLK_FREQ_MHZ) ?
+							(v->DRAMSpeedPerState[i] <= MEM_STROBE_FREQ_MHZ || v->DCFCLKState[i][j] <= DCFCLK_FREQ_EXTRA_PREFETCH_REQ_MHZ) ?
 									mode_lib->vba.ip.min_prefetch_in_strobe_us : 0,
 
 							/* Output */

drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.h

···
 #define BPP_BLENDED_PIPE 0xffffffff
 
 #define MEM_STROBE_FREQ_MHZ 1600
-#define MIN_DCFCLK_FREQ_MHZ 200
+#define DCFCLK_FREQ_EXTRA_PREFETCH_REQ_MHZ 300
 #define MEM_STROBE_MAX_DELIVERY_TIME_US 60.0
 
 struct display_mode_lib;