Disable PL011 UART before configuring it

The PL011 TRM (ARM DDI 0183G) specifies that the UART must be
disabled before any of the control registers are programmed. The
PL011 driver included in TF does not disable the UART, so the
initialization in BL2 and BL31 is violating this requirement
(and potentially in BL1 if the UART is enabled after reset).

This patch modifies the initialization function in the PL011
console driver to disable the UART before programming the
control registers.

Register clobber list and documentation updated.

Fixes ARM-software/tf-issues#300

Change-Id: I839b2d681d48b03f821ac53663a6a78e8b30a1a1

docs/porting-guide.md

@@ -1860,7 +1860,7 @@ they can be invoked without a C Runtime stack.
     Return   : int
 
 This API is used by the crash reporting mechanism to initialize the crash
-console. It should only use the general purpose registers x0 to x2 to do the
+console. It must only use the general purpose registers x0 to x4 to do the
 initialization and returns 1 on success.
 
 ### Function : plat_crash_console_putc
@@ -1869,7 +1869,7 @@ initialization and returns 1 on success.
     Return   : int
 
 This API is used by the crash reporting mechanism to print a character on the
-designated crash console. It should only use general purpose registers x1 and
+designated crash console. It must only use general purpose registers x1 and
 x2 to do its work. The parameter and the return value are in general purpose
 register x0.
 

drivers/arm/pl011/pl011_console.S

@@ -54,7 +54,7 @@
 	 *     w1 - Uart clock in Hz
 	 *     w2 - Baud rate
 	 * Out: return 1 on success else 0 on error
-	 * Clobber list : x1, x2
+	 * Clobber list : x1, x2, x3, x4
 	 * -----------------------------------------------
 	 */
 func console_core_init
@@ -64,6 +64,20 @@ func console_core_init
 	/* Check baud rate and uart clock for sanity */
 	cbz	w1, core_init_fail
 	cbz	w2, core_init_fail
+	/* Disable uart before programming */
+	ldr	w3, [x0, #UARTCR]
+	mov	w4, #PL011_UARTCR_UARTEN
+	bic	w3, w3, w4
+	str	w3, [x0, #UARTCR]
+	/* Flush the transmit FIFO */
+	ldr	w3, [x0, #UARTLCR_H]
+	mov	w4, #PL011_UARTLCR_H_FEN
+	bic	w3, w3, w4
+	str	w3, [x0, #UARTLCR_H]
+	/* Wait for the end of Tx of current character */
+busy_loop:
+	ldr	w3, [x0, #UARTFR]
+	tbnz	w3, #PL011_UARTFR_BUSY_BIT, busy_loop
 	/* Program the baudrate */
 	/* Divisor =  (Uart clock * 4) / baudrate */
 	lsl	w1, w1, #2

drivers/console/console.S

@@ -54,7 +54,7 @@
 	 *     w1 - Uart clock in Hz
 	 *     w2 - Baud rate
 	 * out: return 1 on success else 0 on error
-	 * Clobber list : x1 - x3
+	 * Clobber list : x1 - x4
 	 * -----------------------------------------------
 	 */
 func console_init

include/drivers/arm/pl011.h

@@ -71,6 +71,7 @@
 
 #define PL011_UARTFR_TXFF_BIT	5	/* Transmit FIFO full bit in UARTFR register */
 #define PL011_UARTFR_RXFE_BIT	4	/* Receive FIFO empty bit in UARTFR register */
+#define PL011_UARTFR_BUSY_BIT	3	/* UART busy bit in UARTFR register */
 
 /* Control reg bits */
 #if !PL011_GENERIC_UART

plat/arm/common/aarch64/arm_helpers.S

@@ -66,7 +66,7 @@ endfunc plat_arm_calc_core_pos
 	 * int plat_crash_console_init(void)
 	 * Function to initialize the crash console
 	 * without a C Runtime to print crash report.
-	 * Clobber list : x0, x1, x2
+	 * Clobber list : x0 - x4
 	 * ---------------------------------------------
 	 */
 func plat_crash_console_init

plat/mediatek/mt8173/aarch64/plat_helpers.S

@@ -63,7 +63,7 @@ endfunc platform_is_primary_cpu
 	 * int plat_crash_console_init(void)
 	 * Function to initialize the crash console
 	 * without a C Runtime to print crash report.
-	 * Clobber list : x0, x1, x2
+	 * Clobber list : x0 - x4
 	 * ---------------------------------------------
 	 */
 func plat_crash_console_init

plat/nvidia/tegra/common/aarch64/tegra_helpers.S

@@ -186,7 +186,7 @@ endfunc platform_mem_init
 	 * int plat_crash_console_init(void)
 	 * Function to initialize the crash console
 	 * without a C Runtime to print crash report.
-	 * Clobber list : x0, x1, x2
+	 * Clobber list : x0 - x4
 	 * ---------------------------------------------
 	 */
 func plat_crash_console_init