clk: rockchip: rk3308: Support reading UART rate and clock registers

Add support to read RK3308 registers used to configure UART clocks, and
thus to get UART rate and baudrate. This fixes clock_get_rate returning
error on serial device probing. Moreover, there is no need anymore to
use 'clock-frequency' property for UART nodes in *-u-boot.dtsi files
for all cases where UART is not inited by U-Boot proper or by SPL o by
TPL code but by a preliminary external boot phase (for Rock PI S, UART
is inited by external TPL).

Signed-off-by: Massimo Pegorer <massimo.pegorer+oss@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/dts/rk3308-rock-pi-s-u-boot.dtsi b/arch/arm/dts/rk3308-rock-pi-s-u-boot.dtsi
index 09694b4..6141555 100644
--- a/arch/arm/dts/rk3308-rock-pi-s-u-boot.dtsi
+++ b/arch/arm/dts/rk3308-rock-pi-s-u-boot.dtsi
@@ -12,6 +12,4 @@
 
 &uart0 {
 	bootph-all;
-	clock-frequency = <24000000>;
-	status = "okay";
 };
diff --git a/arch/arm/include/asm/arch-rk3308/cru_rk3308.h b/arch/arm/include/asm/arch-rk3308/cru_rk3308.h
index 86c906b..84b63e4 100644
--- a/arch/arm/include/asm/arch-rk3308/cru_rk3308.h
+++ b/arch/arm/include/asm/arch-rk3308/cru_rk3308.h
@@ -189,6 +189,21 @@
 	DCLK_VOP_DIV_SHIFT	= 0,
 	DCLK_VOP_DIV_MASK	= 0xff,
 
+	/* CRU_CLKSEL_CON10 */
+	/* CRU_CLKSEL_CON13 */
+	/* CRU_CLKSEL_CON16 */
+	/* CRU_CLKSEL_CON19 */
+	/* CRU_CLKSEL_CON22 */
+	CLK_UART_PLL_SEL_SHIFT		= 13,
+	CLK_UART_PLL_SEL_MASK		= 0x7 << CLK_UART_PLL_SEL_SHIFT,
+	CLK_UART_PLL_SEL_DPLL		= 0,
+	CLK_UART_PLL_SEL_VPLL0,
+	CLK_UART_PLL_SEL_VPLL1,
+	CLK_UART_PLL_SEL_480M,
+	CLK_UART_PLL_SEL_24M,
+	CLK_UART_DIV_CON_SHIFT		= 0,
+	CLK_UART_DIV_CON_MASK		= 0x1f << CLK_UART_DIV_CON_SHIFT,
+
 	/* CRU_CLK_SEL25_CON */
 	/* CRU_CLK_SEL26_CON */
 	/* CRU_CLK_SEL27_CON */