tegra: add clock_ll_start_uart() to enable UART prior to reloc

Most boards will want to enable a UART early. This function provides
that feature in Tegra architecture code so the code does not need to be
copied on every board.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

arch/arm/cpu/armv7/tegra2/clock.c

@@ -904,6 +904,20 @@ static int clock_set_rate(enum clock_id clkid, u32 n, u32 m, u32 p, u32 cpcon)
 	return 0;
 }
 
+void clock_ll_start_uart(enum periph_id periph_id)
+{
+	/* Assert UART reset and enable clock */
+	reset_set_enable(periph_id, 1);
+	clock_enable(periph_id);
+	clock_ll_set_source(periph_id, 0); /* UARTx_CLK_SRC = 00, PLLP_OUT0 */
+
+	/* wait for 2us */
+	udelay(2);
+
+	/* De-assert reset to UART */
+	reset_set_enable(periph_id, 0);
+}
+
 int clock_verify(void)
 {
 	struct clk_pll *pll = get_pll(CLOCK_ID_PERIPH);

arch/arm/include/asm/arch-tegra2/clock.h

@@ -344,6 +344,17 @@ unsigned clock_adjust_periph_pll_div(enum periph_id periph_id,
  */
 unsigned clock_get_rate(enum clock_id clkid);
 
+/**
+ * Start up a UART using low-level calls
+ *
+ * Prior to relocation clock_start_periph_pll() cannot be called. This
+ * function provides a way to set up a UART using low-level calls which
+ * do not require BSS.
+ *
+ * @param periph_id	Peripheral ID of UART to enable (e,g, PERIPH_ID_UART1)
+ */
+void clock_ll_start_uart(enum periph_id periph_id);
+
 /*
  * Checks that clocks are valid and prints a warning if not
  *