drivers: ti: uart: introduce UART 16550 driver

This patch introduces a console driver for the TI UART 16550
device.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
Change-Id: I46c1abacfe3c2392aee68f0f94b98a284568ddd8

2 files changed, 244 insertions, 0 deletions

diff --git a/drivers/ti/uart/aarch64/16550_console.S b/drivers/ti/uart/aarch64/16550_console.S
new file mode 100644
index 0000000..616333a
--- /dev/null
+++ b/drivers/ti/uart/aarch64/16550_console.S
@@ -0,0 +1,172 @@
+/*
+ * Copyright (c) 2020, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <arch.h>
+#include <asm_macros.S>
+#include <drivers/console.h>
+#include <drivers/ti/uart/uart_16550.h>
+
+	/*
+	 * "core" functions are low-level implementations that don't require
+	 * writable memory and are thus safe to call in BL1 crash context.
+	 */
+	.globl console_init
+	.globl console_putc
+	.globl console_getc
+	.globl console_flush
+
+	/*
+	 *  The console base is in the data section and not in .bss
+	 *  even though it is zero-init. In particular, this allows
+	 *  the console functions to start using this variable before
+	 *  the runtime memory is initialized for images which do not
+	 *  need to copy the .data section from ROM to RAM.
+	 */
+	.section .data.console_base
+	.align 3
+console_base:
+	.quad 0x0
+
+	/* -----------------------------------------------
+	 * int console_init(uintptr_t base_addr,
+	 * unsigned int uart_clk, unsigned int baud_rate)
+	 * Function to initialize the console without a
+	 * C Runtime to print debug information. This
+	 * function will be accessed by console_init and
+	 * crash reporting.
+	 * In: x0 - console base address
+	 *     w1 - Uart clock in Hz
+	 *     w2 - Baud rate
+	 * Out: return 1 on success, 0 on error
+	 * Clobber list : x1, x2, x3
+	 * -----------------------------------------------
+	 */
+func console_init
+	/* Check the input base address */
+	cbz	x0, init_fail
+	/* Check baud rate and uart clock for sanity */
+	cbz	w1, init_fail
+	cbz	w2, init_fail
+
+	adr	x3, console_base
+	str	x0, [x3]
+
+	/* Program the baudrate */
+	/* Divisor =  Uart clock / (16 * baudrate) */
+	lsl	w2, w2, #4
+	udiv	w2, w1, w2
+	and	w1, w2, #0xff		/* w1 = DLL */
+	lsr	w2, w2, #8
+	and	w2, w2, #0xff		/* w2 = DLLM */
+	ldr	w3, [x0, #UARTLCR]
+	orr	w3, w3, #UARTLCR_DLAB
+	str	w3, [x0, #UARTLCR]	/* enable DLL, DLLM programming */
+	str	w1, [x0, #UARTDLL]	/* program DLL */
+	str	w2, [x0, #UARTDLLM]	/* program DLLM */
+	mov	w2, #~UARTLCR_DLAB
+	and	w3, w3, w2
+	str	w3, [x0, #UARTLCR]	/* disable DLL, DLLM programming */
+
+	/* 8n1 */
+	mov	w3, #3
+	str	w3, [x0, #UARTLCR]
+	/* no interrupt */
+	mov	w3, #0
+	str	w3, [x0, #UARTIER]
+#ifdef TI_16550_MDR_QUIRK
+	/* UART must be enabled on some platforms via the MDR register */
+	str	w3, [x0, #UARTMDR1]
+#endif /* TI_16550_MDR_QUIRK */
+	/* enable fifo, DMA */
+	mov	w3, #(UARTFCR_FIFOEN | UARTFCR_DMAEN)
+	str	w3, [x0, #UARTFCR]
+	/* DTR + RTS */
+	mov	w3, #3
+	str	w3, [x0, #UARTMCR]
+	mov	w0, #1
+	ret
+init_fail:
+	mov	w0, #0
+	ret
+endfunc console_init
+
+	/* --------------------------------------------------------
+	 * int console_putc(int c)
+	 * Function to output a character over the console. It
+	 * returns the character printed on success or -1 on error.
+	 * In : w0 - character to be printed
+	 * Out : return -1 on error else return character.
+	 * Clobber list : x1, x2
+	 * --------------------------------------------------------
+	 */
+func console_putc
+	adr	x1, console_base
+	ldr	x1, [x1]
+
+	/* Prepend '\r' to '\n' */
+	cmp	w0, #0xA
+	b.ne	2f
+	/* Check if the transmit FIFO is full */
+1:	ldr	w2, [x1, #UARTLSR]
+	and	w2, w2, #(UARTLSR_TEMT | UARTLSR_THRE)
+	cmp	w2, #(UARTLSR_TEMT | UARTLSR_THRE)
+	b.ne	1b
+	mov	w2, #0xD		/* '\r' */
+	str	w2, [x1, #UARTTX]
+
+	/* Check if the transmit FIFO is full */
+2:	ldr	w2, [x1, #UARTLSR]
+	and	w2, w2, #(UARTLSR_TEMT | UARTLSR_THRE)
+	cmp	w2, #(UARTLSR_TEMT | UARTLSR_THRE)
+	b.ne	2b
+	str	w0, [x1, #UARTTX]
+	ret
+endfunc console_putc
+
+	/* ---------------------------------------------
+	 * int console_getc(void)
+	 * Function to get a character from the console.
+	 * It returns the character grabbed on success
+	 * or -1 on if no character is available.
+	 * Out : w0 - character if available, else -1
+	 * Clobber list : x0, x1
+	 * ---------------------------------------------
+	 */
+func console_getc
+	adr	x0, console_base
+	ldr	x0, [x0]
+
+	/* Check if the receive FIFO is empty */
+1:	ldr	w1, [x0, #UARTLSR]
+	tbz	w1, #UARTLSR_RDR_BIT, no_char
+	ldr	w0, [x0, #UARTRX]
+	ret
+no_char:
+	mov	w0, #ERROR_NO_PENDING_CHAR
+	ret
+endfunc console_getc
+
+	/* ---------------------------------------------
+	 * int console_16550_core_flush(uintptr_t base_addr)
+	 * Function to force a write of all buffered
+	 * data that hasn't been output.
+	 * Out : return -1 on error else return 0.
+	 * Clobber list : x0, x1
+	 * ---------------------------------------------
+	 */
+func console_flush
+	adr	x0, console_base
+	ldr	x0, [x0]
+
+	/* Loop until the transmit FIFO is empty */
+1:	ldr	w1, [x0, #UARTLSR]
+	and	w1, w1, #(UARTLSR_TEMT | UARTLSR_THRE)
+	cmp	w1, #(UARTLSR_TEMT | UARTLSR_THRE)
+	b.ne	1b
+
+	mov	w0, #0
+	ret
+endfunc console_flush
diff --git a/include/drivers/ti/uart/uart_16550.h b/include/drivers/ti/uart/uart_16550.h
new file mode 100644
index 0000000..b8c3fdb
--- /dev/null
+++ b/include/drivers/ti/uart/uart_16550.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2020, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef UART_16550_H
+#define UART_16550_H
+
+/* UART16550 Registers */
+#define UARTTX			0x0
+#define UARTRX			0x0
+#define UARTDLL			0x0
+#define UARTIER			0x4
+#define UARTDLLM		0x4
+#define UARTIIR			0x8
+#define UARTFCR			0x8
+#define UARTLCR			0xc
+#define UARTMCR			0x10
+#define UARTLSR			0x14
+#define UARTMSR			0x18
+#define UARTSPR			0x1c
+#define UARTCSR			0x20
+/* Some instances have MDR1 defined as well */
+#define UARTMDR1		0x20
+#define UARTRXFIFOCFG		0x24
+#define UARTMIE			0x28
+#define UARTVNDR		0x2c
+#define UARTASR			0x3c
+
+/* FIFO Control Register bits */
+#define UARTFCR_FIFOMD_16450	(0 << 6)
+#define UARTFCR_FIFOMD_16550	(1 << 6)
+#define UARTFCR_RXTRIG_1	(0 << 6)
+#define UARTFCR_RXTRIG_4	(1 << 6)
+#define UARTFCR_RXTRIG_8	(2 << 6)
+#define UARTFCR_RXTRIG_16	(3 << 6)
+#define UARTFCR_TXTRIG_1	(0 << 4)
+#define UARTFCR_TXTRIG_4	(1 << 4)
+#define UARTFCR_TXTRIG_8	(2 << 4)
+#define UARTFCR_TXTRIG_16	(3 << 4)
+#define UARTFCR_DMAEN		(1 << 3)	/* Enable DMA mode */
+#define UARTFCR_TXCLR		(1 << 2)	/* Clear contents of Tx FIFO */
+#define UARTFCR_RXCLR		(1 << 1)	/* Clear contents of Rx FIFO */
+#define UARTFCR_FIFOEN		(1 << 0)	/* Enable the Tx/Rx FIFO */
+
+/* Line Control Register bits */
+#define UARTLCR_DLAB		(1 << 7)	/* Divisor Latch Access */
+#define UARTLCR_SETB		(1 << 6)	/* Set BREAK Condition */
+#define UARTLCR_SETP		(1 << 5)	/* Set Parity to LCR[4] */
+#define UARTLCR_EVEN		(1 << 4)	/* Even Parity Format */
+#define UARTLCR_PAR		(1 << 3)	/* Parity */
+#define UARTLCR_STOP		(1 << 2)	/* Stop Bit */
+#define UARTLCR_WORDSZ_5	0		/* Word Length of 5 */
+#define UARTLCR_WORDSZ_6	1		/* Word Length of 6 */
+#define UARTLCR_WORDSZ_7	2		/* Word Length of 7 */
+#define UARTLCR_WORDSZ_8	3		/* Word Length of 8 */
+
+/* Line Status Register bits */
+#define UARTLSR_RXFIFOEMT	(1 << 9)	/* Rx Fifo Empty */
+#define UARTLSR_TXFIFOFULL	(1 << 8)	/* Tx Fifo Full */
+#define UARTLSR_RXFIFOERR	(1 << 7)	/* Rx Fifo Error */
+#define UARTLSR_TEMT		(1 << 6)	/* Tx Shift Register Empty */
+#define UARTLSR_THRE		(1 << 5)	/* Tx Holding Register Empty */
+#define UARTLSR_BRK		(1 << 4)	/* Break Condition Detected */
+#define UARTLSR_FERR		(1 << 3)	/* Framing Error */
+#define UARTLSR_PERR		(1 << 3)	/* Parity Error */
+#define UARTLSR_OVRF		(1 << 2)	/* Rx Overrun Error */
+#define UARTLSR_RDR_BIT		(0)		/* Rx Data Ready Bit */
+#define UARTLSR_RDR		(1 << UARTLSR_RDR_BIT)	/* Rx Data Ready */
+
+#endif /* UART_16550_H */