clk: starfive: jh7100: Handle audio_div clock properly

It turns out the audio_div clock is a fractional divider where the
lowest byte of the ctrl register is the integer part of the divider and
the 2nd byte is the number of 100th added to the divider.

The children of this clock is used by the audio peripherals for their
sample rate clock, so round to the closest possible rate rather than
always rounding down like regular dividers.

Fixes: 4210be66 ("clk: starfive: Add JH7100 clock generator driver")
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Link: https://lore.kernel.org/r/20220126173953.1016706-3-kernel@esmil.dkSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/starfive/clk-starfive-jh7100.c

@@ -32,6 +32,13 @@
 #define JH7100_CLK_MUX_MASK	GENMASK(27, 24)
 #define JH7100_CLK_MUX_SHIFT	24
 #define JH7100_CLK_DIV_MASK	GENMASK(23, 0)
+#define JH7100_CLK_FRAC_MASK	GENMASK(15, 8)
+#define JH7100_CLK_FRAC_SHIFT	8
+#define JH7100_CLK_INT_MASK	GENMASK(7, 0)
+
+/* fractional divider min/max */
+#define JH7100_CLK_FRAC_MIN	100UL
+#define JH7100_CLK_FRAC_MAX	25599UL
 
 /* clock data */
 #define JH7100_GATE(_idx, _name, _flags, _parent) [_idx] = {		\
@@ -55,6 +62,13 @@
 	.parents = { [0] = _parent },					\
 }
 
+#define JH7100_FDIV(_idx, _name, _parent) [_idx] = {			\
+	.name = _name,							\
+	.flags = 0,							\
+	.max = JH7100_CLK_FRAC_MAX,					\
+	.parents = { [0] = _parent },					\
+}
+
 #define JH7100__MUX(_idx, _name, _nparents, ...) [_idx] = {		\
 	.name = _name,							\
 	.flags = 0,							\
@@ -225,7 +239,7 @@ static const struct {
 	JH7100__MUX(JH7100_CLK_USBPHY_25M, "usbphy_25m", 2,
 		    JH7100_CLK_OSC_SYS,
 		    JH7100_CLK_USBPHY_PLLDIV25M),
-	JH7100__DIV(JH7100_CLK_AUDIO_DIV, "audio_div", 131072, JH7100_CLK_AUDIO_ROOT),
+	JH7100_FDIV(JH7100_CLK_AUDIO_DIV, "audio_div", JH7100_CLK_AUDIO_ROOT),
 	JH7100_GATE(JH7100_CLK_AUDIO_SRC, "audio_src", 0, JH7100_CLK_AUDIO_DIV),
 	JH7100_GATE(JH7100_CLK_AUDIO_12288, "audio_12288", 0, JH7100_CLK_OSC_AUD),
 	JH7100_GDIV(JH7100_CLK_VIN_SRC, "vin_src", 0, 4, JH7100_CLK_VIN_ROOT),
@@ -440,6 +454,49 @@ static int jh7100_clk_set_rate(struct clk_hw *hw,
 	return 0;
 }
 
+static unsigned long jh7100_clk_frac_recalc_rate(struct clk_hw *hw,
+						 unsigned long parent_rate)
+{
+	struct jh7100_clk *clk = jh7100_clk_from(hw);
+	u32 reg = jh7100_clk_reg_get(clk);
+	unsigned long div100 = 100 * (reg & JH7100_CLK_INT_MASK) +
+			       ((reg & JH7100_CLK_FRAC_MASK) >> JH7100_CLK_FRAC_SHIFT);
+
+	return (div100 >= JH7100_CLK_FRAC_MIN) ? 100 * parent_rate / div100 : 0;
+}
+
+static int jh7100_clk_frac_determine_rate(struct clk_hw *hw,
+					  struct clk_rate_request *req)
+{
+	unsigned long parent100 = 100 * req->best_parent_rate;
+	unsigned long rate = clamp(req->rate, req->min_rate, req->max_rate);
+	unsigned long div100 = clamp(DIV_ROUND_CLOSEST(parent100, rate),
+				     JH7100_CLK_FRAC_MIN, JH7100_CLK_FRAC_MAX);
+	unsigned long result = parent100 / div100;
+
+	/* clamp the result as in jh7100_clk_determine_rate() above */
+	if (result > req->max_rate && div100 < JH7100_CLK_FRAC_MAX)
+		result = parent100 / (div100 + 1);
+	if (result < req->min_rate && div100 > JH7100_CLK_FRAC_MIN)
+		result = parent100 / (div100 - 1);
+
+	req->rate = result;
+	return 0;
+}
+
+static int jh7100_clk_frac_set_rate(struct clk_hw *hw,
+				    unsigned long rate,
+				    unsigned long parent_rate)
+{
+	struct jh7100_clk *clk = jh7100_clk_from(hw);
+	unsigned long div100 = clamp(DIV_ROUND_CLOSEST(100 * parent_rate, rate),
+				     JH7100_CLK_FRAC_MIN, JH7100_CLK_FRAC_MAX);
+	u32 value = ((div100 % 100) << JH7100_CLK_FRAC_SHIFT) | (div100 / 100);
+
+	jh7100_clk_reg_rmw(clk, JH7100_CLK_DIV_MASK, value);
+	return 0;
+}
+
 static u8 jh7100_clk_get_parent(struct clk_hw *hw)
 {
 	struct jh7100_clk *clk = jh7100_clk_from(hw);
@@ -526,6 +583,13 @@ static const struct clk_ops jh7100_clk_div_ops = {
 	.debug_init = jh7100_clk_debug_init,
 };
 
+static const struct clk_ops jh7100_clk_fdiv_ops = {
+	.recalc_rate = jh7100_clk_frac_recalc_rate,
+	.determine_rate = jh7100_clk_frac_determine_rate,
+	.set_rate = jh7100_clk_frac_set_rate,
+	.debug_init = jh7100_clk_debug_init,
+};
+
 static const struct clk_ops jh7100_clk_gdiv_ops = {
 	.enable = jh7100_clk_enable,
 	.disable = jh7100_clk_disable,
@@ -564,6 +628,8 @@ static const struct clk_ops *__init jh7100_clk_ops(u32 max)
 	if (max & JH7100_CLK_DIV_MASK) {
 		if (max & JH7100_CLK_ENABLE)
 			return &jh7100_clk_gdiv_ops;
+		if (max == JH7100_CLK_FRAC_MAX)
+			return &jh7100_clk_fdiv_ops;
 		return &jh7100_clk_div_ops;
 	}