drm/amd/display: Add switch for Fractional PWM on or off

[Why]
Some LED Driver might not like Fractional PWM especially at extreme
ranges near 0% or 100%.
For example, backlight flashing could be observed.
We want a way to switch fractional PWM on/off either for debug, or
possibly production.

[How]
Add DC code that can send new FW command to enable/disable
fractional PWM.
Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -183,6 +183,7 @@ struct dc_config {
 	bool disable_disp_pll_sharing;
 	bool fbc_support;
 	bool optimize_edp_link_rate;
+	bool disable_fractional_pwm;
 	bool allow_seamless_boot_optimization;
 };
 

drivers/gpu/drm/amd/display/dc/dce/dce_abm.c

@@ -50,6 +50,7 @@
 #define MCP_ABM_LEVEL_SET 0x65
 #define MCP_ABM_PIPE_SET 0x66
 #define MCP_BL_SET 0x67
+#define MCP_BL_SET_PWM_FRAC     0x6A  /* Enable or disable Fractional PWM */
 
 #define MCP_DISABLE_ABM_IMMEDIATELY 255
 
@@ -390,6 +391,23 @@ static bool dce_abm_init_backlight(struct abm *abm)
 	REG_UPDATE(BL_PWM_GRP1_REG_LOCK,
 			BL_PWM_GRP1_REG_LOCK, 0);
 
+	/* Wait until microcontroller is ready to process interrupt */
+	REG_WAIT(MASTER_COMM_CNTL_REG, MASTER_COMM_INTERRUPT, 0, 100, 800);
+
+	/* Set PWM fractional enable/disable */
+	value = (abm->ctx->dc->config.disable_fractional_pwm == false) ? 1 : 0;
+	REG_WRITE(MASTER_COMM_DATA_REG1, value);
+
+	/* Set command to enable or disable fractional PWM microcontroller */
+	REG_UPDATE(MASTER_COMM_CMD_REG, MASTER_COMM_CMD_REG_BYTE0,
+			MCP_BL_SET_PWM_FRAC);
+
+	/* Notify microcontroller of new command */
+	REG_UPDATE(MASTER_COMM_CNTL_REG, MASTER_COMM_INTERRUPT, 1);
+
+	/* Ensure command has been executed before continuing */
+	REG_WAIT(MASTER_COMM_CNTL_REG, MASTER_COMM_INTERRUPT, 0, 100, 800);
+
 	return true;
 }