drm/sun4i: Create minimal multipliers and dividers

The various outputs the TCON can provide have different constraints on the
dotclock divider. Let's make them configurable by the various mode_set
functions.
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/92ff5881c8f8674056d34458b2f264cd48d4e136.1513854122.git-series.maxime.ripard@free-electrons.com

drivers/gpu/drm/sun4i/sun4i_dotclock.c

@@ -17,8 +17,9 @@
 #include "sun4i_dotclock.h"
 
 struct sun4i_dclk {
-	struct clk_hw	hw;
-	struct regmap	*regmap;
+	struct clk_hw		hw;
+	struct regmap		*regmap;
+	struct sun4i_tcon	*tcon;
 };
 
 static inline struct sun4i_dclk *hw_to_dclk(struct clk_hw *hw)
@@ -73,11 +74,13 @@ static unsigned long sun4i_dclk_recalc_rate(struct clk_hw *hw,
 static long sun4i_dclk_round_rate(struct clk_hw *hw, unsigned long rate,
 				  unsigned long *parent_rate)
 {
+	struct sun4i_dclk *dclk = hw_to_dclk(hw);
+	struct sun4i_tcon *tcon = dclk->tcon;
 	unsigned long best_parent = 0;
 	u8 best_div = 1;
 	int i;
 
-	for (i = 6; i <= 127; i++) {
+	for (i = tcon->dclk_min_div; i <= tcon->dclk_max_div; i++) {
 		unsigned long ideal = rate * i;
 		unsigned long rounded;
 
@@ -167,6 +170,7 @@ int sun4i_dclk_create(struct device *dev, struct sun4i_tcon *tcon)
 	dclk = devm_kzalloc(dev, sizeof(*dclk), GFP_KERNEL);
 	if (!dclk)
 		return -ENOMEM;
+	dclk->tcon = tcon;
 
 	init.name = clk_name;
 	init.ops = &sun4i_dclk_ops;

drivers/gpu/drm/sun4i/sun4i_tcon.c

@@ -177,6 +177,8 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
 	u8 clk_delay;
 	u32 val = 0;
 
+	tcon->dclk_min_div = 6;
+	tcon->dclk_max_div = 127;
 	sun4i_tcon0_mode_set_common(tcon, mode);
 
 	/* Adjust clock delay */

drivers/gpu/drm/sun4i/sun4i_tcon.h

@@ -169,6 +169,8 @@ struct sun4i_tcon {
 
 	/* Pixel clock */
 	struct clk			*dclk;
+	u8				dclk_max_div;
+	u8				dclk_min_div;
 
 	/* Reset control */
 	struct reset_control		*lcd_rst;