serial: tegra: Support for best clock source

Finding the best clock source for uart controller which can
generate the clock rate having minimum error between requested
baudrate and configured baudrate.

bug 837140
bug 836059

Change-Id: I4e751b238612a21d894ee8e6611886ab6e832a36
Reviewed-on: http://git-master/r/37635
Tested-by: Rakesh Goyal <rgoyal@nvidia.com>
Reviewed-by: Aleksandr Frid <afrid@nvidia.com>
Reviewed-by: Pradeep Goudagunta <pgoudagunta@nvidia.com>
Tested-by: Pradeep Goudagunta <pgoudagunta@nvidia.com>
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>

1 files changed, 107 insertions, 2 deletions

diff --git a/drivers/serial/tegra_hsuart.c b/drivers/serial/tegra_hsuart.c
index 0315a152beca..e7b8d2723619 100644
--- a/drivers/serial/tegra_hsuart.c
+++ b/drivers/serial/tegra_hsuart.c
@@ -1001,8 +1001,110 @@ static void tegra_enable_ms(struct uart_port *u)
 {
 }
 
-#define UART_CLOCK_ACCURACY 5
+#ifndef CONFIG_ARCH_TEGRA_2x_SOC
+static int clk_div71_get_divider(unsigned long parent_rate,
+		unsigned long rate)
+{
+	s64 divider_u71 = parent_rate;
+	if (!rate)
+		return -EINVAL;
+
+	divider_u71 *= 2;
+	divider_u71 += rate - 1;
+	do_div(divider_u71, rate);
+
+	if ((divider_u71 - 2) < 0)
+		return 0;
+
+	if ((divider_u71 - 2) > 255)
+		return -EINVAL;
+
+	return divider_u71 - 2;
+}
+#endif
+
+static int clk_div16_get_divider(unsigned long parent_rate, unsigned long rate)
+{
+	s64 divider_u16;
+
+	divider_u16 = parent_rate;
+	if (!rate)
+		return -EINVAL;
+	divider_u16 += rate - 1;
+	do_div(divider_u16, rate);
+
+	if (divider_u16 > 0xFFFF)
+		return -EINVAL;
+
+	return divider_u16;
+}
 
+static unsigned long find_best_clock_source(struct tegra_uart_port *t,
+		unsigned long rate)
+{
+	struct uart_port *u = &t->uport;
+	struct tegra_uart_platform_data *pdata;
+	int i;
+	int divider;
+	unsigned long parent_rate;
+	unsigned long new_rate;
+	unsigned long err_rate;
+	unsigned int fin_err = rate;
+	unsigned long fin_rate = rate;
+	int final_index = -1;
+	int count;
+
+	pdata = u->dev->platform_data;
+	if (!pdata || !pdata->parent_clk_count)
+		return fin_rate;
+
+	for (count = 0; count < pdata->parent_clk_count; ++count) {
+		parent_rate = pdata->parent_clk_list[count].fixed_clk_rate;
+
+#ifndef CONFIG_ARCH_TEGRA_2x_SOC
+		divider = clk_div71_get_divider(parent_rate, rate);
+
+		/* Get the best divider around calculated value */
+		if (divider > 2) {
+			for (i = divider - 2; i < (divider + 2); ++i) {
+				new_rate = ((parent_rate << 1) + i + 1) /
+								(i + 2);
+				err_rate = abs(new_rate - rate);
+				if (err_rate < fin_err) {
+					final_index = count;
+					fin_err = err_rate;
+					fin_rate = new_rate;
+				}
+			}
+		}
+#endif
+		/* Get the divisor by uart controller dll/dlm */
+		divider = clk_div16_get_divider(parent_rate, rate);
+
+		/* Get the best divider around calculated value */
+		if (divider > 2) {
+			for (i = divider - 2; i < (divider + 2); ++i) {
+				new_rate = parent_rate/i;
+				err_rate = abs(new_rate - rate);
+				if (err_rate < fin_err) {
+					final_index = count;
+					fin_err = err_rate;
+					fin_rate = parent_rate;
+				}
+			}
+		}
+	}
+
+	if (final_index >= 0) {
+		dev_info(t->uport.dev, "Setting clk_src %s\n",
+				pdata->parent_clk_list[final_index].name);
+		clk_set_parent(t->clk,
+			pdata->parent_clk_list[final_index].parent_clk);
+	}
+	return fin_rate;
+}
+
+#define UART_CLOCK_ACCURACY 5
 static void tegra_set_baudrate(struct tegra_uart_port *t, unsigned int baud)
 {
 	unsigned long rate;
@@ -1010,12 +1112,15 @@ static void tegra_set_baudrate(struct tegra_uart_port *t, unsigned int baud)
 	unsigned char lcr;
 	unsigned int baud_actual;
 	unsigned int baud_delta;
+	unsigned long best_rate;
 
 	if (t->baud == baud)
 		return;
 
 	rate = baud * 16;
-	clk_set_rate(t->clk, rate);
+	best_rate = find_best_clock_source(t, rate);
+	clk_set_rate(t->clk, best_rate);
+
 	rate = clk_get_rate(t->clk);
 
 	divisor = rate;