达芬奇DM644X平台(ARM9, Linux-2.6.10)BSP之serial.c浅析

/*
* linux/arch/arm/mach-davinci/serial.c
*
* TI DaVinci serial driver hookup file
*
* Copyright (C) 2006 Texas Instruments.
*
* ----------------------------------------------------------------------------
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
* ----------------------------------------------------------------------------
*
*/

#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/serial_8250.h>
#include <linux/serial_reg.h>
#include <linux/delay.h>

#include <asm/io.h>
#include <asm/irq.h>
#include <asm/hardware.h>
#include <asm/hardware/clock.h>
#include <asm/serial.h>
#include <asm/arch/hardware.h>
#include <asm/arch/irqs.h>
#include <asm/arch/cpu.h>

#define UART_DAVINCI_PWREMU 0x0c

/*
对于DM644x平台来说，该文件的作用只是打开串口0模块的时钟和电源。
DM644x平台的串口采用的是TL16C550工业标准异步通信模块。内核中已经包含
该标准（（8250/16550））串口的驱动的代码：drivers/serial/8250.c。

*/

// 从串口寄存器offset读出值

static inline unsigned int davinci_serial_in(struct plat_serial8250_port *up,
int offset)
{
offset <<= up->regshift;
return (unsigned int)__raw_readb(up->membase + offset);
}

// 向串口寄存器offset写入值value

static inline void davinci_serial_outp(struct plat_serial8250_port *p,
int offset, int value)
{
offset <<= p->regshift;
__raw_writeb(value, p->membase + offset);
}

// 复位串口。UART_DAVINCI_PWREMU寄存器是达芬奇平台专有的，通用的8250串口没有。

static void __init davinci_serial_reset(struct plat_serial8250_port *p)
{
/* reset both transmitter and receiver: bits 14,13 = UTRST, URRST */
unsigned int pwremu = 0;

davinci_serial_outp(p, UART_IER, 0);    /* disable all interrupts */

davinci_serial_outp(p, UART_DAVINCI_PWREMU, pwremu);// 禁止发送和接收，停止UART

mdelay(10);

pwremu |= (0x3 << 13);
pwremu |= 0x1;
// 打开接收和发送，启动UART

davinci_serial_outp(p, UART_DAVINCI_PWREMU, pwremu);
}

#define UART_DM6467_SCR        __REG(DAVINCI_UART0_BASE + 0x40)
/*
* Internal UARTs need to be initialized for the 8250 autoconfig to work
* properly. Note that the TX watermark initialization may not be needed
* once the 8250.c watermark handling code is merged.
*/
static int __init dm646x_serial_reset(void)
{
UART_DM6467_SCR = 0x08;

return 0;
}

/*
串口初始化，打开时钟和电源。
davinci_serial_init()例程由board_evm.c中的board_init()例程调用，后者被
davinci_map_io()例程调用，而其又被注册到board_evm.c中的机器描述符中（struct machine_desc），
故具体调用过程是：
start_kernel()-->setup_arch()-->paging_init()-->mdesc->map_io()
(其就是davinci_map_io())-->board_init()-->davinci_serial_init()。

*/
void __init davinci_serial_init(struct platform_device *pdev)
{
struct clk *uart_clk;
struct device *dev = &pdev->dev;
struct plat_serial8250_port *p;
int uart;
char uart_name[6];

memset(uart_name, 0, sizeof(uart_name));
for (p = dev->platform_data; p && p->flags; p++) {
switch (p->mapbase) {// 获取串口号

case DAVINCI_UART0_BASE:
uart = 0;
break;
case DAVINCI_UART1_BASE:
uart = 1;
break;
case DM644X_UART2_BASE:
case DM355_UART2_BASE:
uart = 2;
break;
default:
dev_err(dev,
"Unknown UART base address 0x%08lx/n",
p->mapbase);
continue;
}
sprintf(uart_name, "UART%i", uart);
uart_clk = clk_get(dev, uart_name);// 获取时钟

if (IS_ERR(uart_clk))
dev_err(dev, "failed to get %s clock/n", uart_name);
else
clk_enable(uart_clk);    // 打开时钟和电源

// 如果是DM355平台，则复位

if (cpu_is_davinci_dm355())
davinci_serial_reset(p);
}
}

late_initcall(dm646x_serial_reset);