clk: meson: add ROUND_CLOSEST to the pll driver

Provide an option for the pll driver to round to the rate closest to the
requested rate, instead of systematically rounding down.

This may allow the provided rate to be closer to the requested rate when
rounding up is not an issue

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

drivers/clk/meson/clk-pll.c

@@ -105,7 +105,12 @@ static u16 __pll_params_with_frac(unsigned long rate,
 	u64 val = (u64)rate * pllt->n;
 
 	val <<= pllt->od + pllt->od2 + pllt->od3;
+
+	if (pll->flags & CLK_MESON_PLL_ROUND_CLOSEST)
+		val = DIV_ROUND_CLOSEST_ULL(val * frac_max, parent_rate);
+	else
 		val = div_u64(val * frac_max, parent_rate);
+
 	val -= pllt->m * frac_max;
 
 	return min((u16)val, (u16)(frac_max - 1));
@@ -125,9 +130,13 @@ meson_clk_get_pll_settings(unsigned long rate,
 	while (table[i].rate && table[i].rate <= rate)
 		i++;
 
-	/* Select the setting of the rounded down rate */
-	if (i != 0)
+	if (i != 0) {
+		if (MESON_PARM_APPLICABLE(&pll->frac) ||
+		    !(pll->flags & CLK_MESON_PLL_ROUND_CLOSEST) ||
+		    (abs(rate - table[i - 1].rate) <
+		     abs(rate - table[i].rate)))
 			i--;
+	}
 
 	return (struct pll_rate_table *)&table[i];
 }

drivers/clk/meson/clkc.h

@@ -71,6 +71,8 @@ struct pll_rate_table {
 		.od		= (_od),				\
 	}
 
+#define CLK_MESON_PLL_ROUND_CLOSEST	BIT(0)
+
 struct meson_clk_pll_data {
 	struct parm m;
 	struct parm n;