本文共 4620 字，大约阅读时间需要 15 分钟。
OK335xS UART设备注册代码跟踪
作为OK335xS Linux内核开发者，在理解UART设备注册过程时，我选择了函数调用线路图进行标记，以便更直观地进行阅读和分析。通过使用vim和ctags工具，我对代码进行了详细的跟踪和解读。
在板级文件中，MACHINE_START和MACHINE_END宏定义用于定义机器启动和结束 macros。以下是板级文件中关键的初始化设置：
MACHINE_START(AM335XEVM, "am335xevm") .atag_offset = 0x100, .map_io = am335x_evm_map_io, .init_early = am33xx_init_early, .init_irq = ti81xx_init_irq, .handle_irq = omap3_intc_handle_irq, .timer = &omap3_am33xx_timer, .init_machine = am335x_evm_init,MACHINE_ENDMACHINE_START(AM335XIAEVM, "am335xiaevm") .atag_offset = 0x100, .map_io = am335x_evm_map_io, .init_early = am33xx_init_early, .init_irq = ti81xx_init_irq, .timer = &omap3_am33xx_timer, .init_machine = am335x_evm_init,MACHINE_END
am33xx_init_early函数是内核初始化的一个重要步骤，主要完成以下任务：
void __init am33xx_init_early(void){ omap2_set_globals_am33xx(); omap3xxx_check_revision(); am33xx_check_features(); omap_common_init_early(); am33xx_voltagedomains_init(); omap44xx_prminst_init(); am33xx_powerdomains_init(); omap44xx_cminst_init(); am33xx_clockdomains_init(); am33xx_hwmod_init(); omap_hwmod_init_postsetup(); omap3xxx_clk_init();} 在这个过程中， omap2_set_globals_am33xx()用于设置全局配置， omap3xxx_check_revision()用于检查处理器版本， am33xx_check_features()用于检测硬件功能等。
am335x_evm_init函数是板级初始化函数，主要负责板级硬件的初始化配置：
static void __init am335x_evm_init(void){ am33xx_cpuidle_init(); am33xx_mux_init(board_mux); omap_serial_init(); am335x_evm_i2c_init(); omap_sdrc_init(NULL, NULL); usb_musb_init(&musb_board_data); omap_board_config = am335x_evm_config; omap_board_config_size = ARRAY_SIZE(am335x_evm_config); if (clk_add_alias("pruss", NULL, "pruss_uart_gclk", NULL)) pr_warn("failed to create an alias: icss_uart_gclk --> pruss\n"); if (clk_add_alias("sgx_ck", NULL, "gfx_fclk", NULL)) pr_warn("failed to create an alias: gfx_fclk --> sgx_ck\n"); printk("zengjf test code 1.\n");} omap_serial_init()函数负责初始化串口设备，am335x_evm_i2c_init()函数负责初始化I2C总线。
UART设备的注册过程主要通过 omap_hwmod_register()函数完成。以下是相关代码片段：
int __init omap_hwmod_register(struct omap_hwmod **ohs){ int r, i; if (!ohs) return 0; i = 0; do { r = _register(ohs[i]); WARN(r, "omap_hwmod: %s: _register returned %d\n", ohs[i]->name, r); } while (ohs[++i]); return 0;}static int __init _register(struct omap_hwmod *oh){ int ms_id; if (!oh || !oh->name || !oh->class || !oh->class->name || (oh->_state != _HWMOD_STATE_UNKNOWN)) return -EINVAL; pr_debug("omap_hwmod: %s: registering\n", oh->name); if (_lookup(oh->name)) return -EEXIST; ms_id = _find_mpu_port_index(oh); if (!IS_ERR_VALUE(ms_id)) oh->_mpu_port_index = ms_id; else oh->_int_flags |= _HWMOD_NO_MPU_PORT; list_add_tail(&oh->node, &omap_hwmod_list); spin_lock_init(&oh->_lock); oh->_state = _HWMOD_STATE_REGISTERED; if (!strcmp(oh->name, MPU_INITIATOR_NAME)) mpu_oh = oh; return 0;} UART设备的初始化主要通过 omap_serial_init_port()和 omap_serial_early_init()函数完成。以下是相关代码片段：
void __init omap_serial_init(void){ omap_serial_board_init(NULL);}void __init omap_serial_board_init(struct omap_uart_port_info *info){ struct omap_uart_state *uart; struct omap_board_data bdata; list_for_each_entry(uart, &uart_list, node) { bdata.id = uart->num; bdata.flags = 0; bdata.pads = NULL; bdata.pads_cnt = 0; if (cpu_is_omap44xx() || (cpu_is_omap34xx() && !cpu_is_am33xx())) omap_serial_fill_default_pads(&bdata); if (!info) omap_serial_init_port(&bdata, NULL); else omap_serial_init_port(&bdata, &info[uart->num]); }} 平台设备构建主要通过 omap_device_build()函数完成。以下是相关代码片段：
struct platform_device *omap_device_build(const char *pdev_name, int pdev_id, struct omap_hwmod *oh, void *pdata, int pdata_len, struct omap_device_pm_latency *pm_lats, int pm_lats_cnt, int is_early_device){ struct omap_hwmod *ohs[] = { oh }; if (!oh) return ERR_PTR(-EINVAL); return omap_device_build_ss(pdev_name, pdev_id, ohs, 1, pdata, pdata_len, pm_lats, pm_lats_cnt, is_early_device);} 早期设备注册主要通过 omap_early_device_register()函数完成：
static int omap_early_device_register(struct platform_device *pdev){ struct platform_device *devices[1]; devices[0] = pdev; early_platform_add_devices(devices, 1); return 0;} 通过以上代码分析，可以清晰地看到OK335xS UART设备注册的整体流程和关键函数的作用。
转载地址：http://atsfk.baihongyu.com/