AM335x(TQ335x)学习笔记——u-boot-2014.10移植

最近移植了下u-boot-2014.10到TQ335x，如果基于am335x evm进行移植，需要修改的地方并不多。

由于TI的am335x evm开发使用了一个eeprom保存了板载配置信息，用来区分不同板子的型号的，而TQ335x没有这个eeprom，因此，需要修改eeprom相关的部分，使u-boot适应TQ335x开发板。

使用source insight查看代码，很容易发现，所有获取板载配置的部分都是通过读取eeprom获得的，因此，首选修改read_eeprom（board/ti/am335x/board.c）函数，具体的修改如下：

static int read_eeprom(struct am335x_baseboard_id *header)
{
#if 1
    strcpy(header->name, "TQ335x");
#else
    /* Check if baseboard eeprom is available */
    if (i2c_probe(CONFIG_SYS_I2C_EEPROM_ADDR)) {
        puts("Could not probe the EEPROM; something fundamentally "
            "wrong on the I2C bus.\n");
        return -ENODEV;
    }

    /* read the eeprom using i2c */
    if (i2c_read(CONFIG_SYS_I2C_EEPROM_ADDR, 0, 2, (uchar *)header,
             sizeof(struct am335x_baseboard_id))) {
        puts("Could not read the EEPROM; something fundamentally"
            " wrong on the I2C bus.\n");
        return -EIO;
    }

    if (header->magic != 0xEE3355AA) {
        /*
         * read the eeprom using i2c again,
         * but use only a 1 byte address
         */
        if (i2c_read(CONFIG_SYS_I2C_EEPROM_ADDR, 0, 1, (uchar *)header,
                 sizeof(struct am335x_baseboard_id))) {
            puts("Could not read the EEPROM; something "
                "fundamentally wrong on the I2C bus.\n");
            return -EIO;
        }

        if (header->magic != 0xEE3355AA) {
            printf("Incorrect magic number (0x%x) in EEPROM\n",
                    header->magic);
            return -EINVAL;
        }
    }
#endif

    return 0;
}

通过上述修改，u-boot不去读取eeprom，而是直接将header的name赋值为"TQ335x"，后面可以根据这一配置区分是否为TQ335x开发板。

然后是修改get_dpll_ddr_params（board/ti/am335x/board.c）函数，具体的修改内容如下：

const struct dpll_params *get_dpll_ddr_params(void)
{
    struct am335x_baseboard_id header;

    enable_i2c0_pin_mux();
    i2c_init(CONFIG_SYS_OMAP24_I2C_SPEED, CONFIG_SYS_OMAP24_I2C_SLAVE);
    if (read_eeprom(&header) < 0)
        puts("Could not get board ID.\n");

    if (board_is_tq335x(&header) || board_is_evm_sk(&header))
        return &dpll_ddr_evm_sk;
    else if (board_is_bone_lt(&header))
        return &dpll_ddr_bone_black;
    else if (board_is_evm_15_or_later(&header))
        return &dpll_ddr_evm_sk;
    else
        return &dpll_ddr;
}

然后是修改sdram_init（board/ti/am335x/board.c）函数，具体的修改内容如下：

void sdram_init(void)
{
    __maybe_unused struct am335x_baseboard_id header;

    if (read_eeprom(&header) < 0)
        puts("Could not get board ID.\n");

    if (board_is_evm_sk(&header)) {
        /*
         * EVM SK 1.2A and later use gpio0_7 to enable DDR3.
         * This is safe enough to do on older revs.
         */
        gpio_request(GPIO_DDR_VTT_EN, "ddr_vtt_en");
        gpio_direction_output(GPIO_DDR_VTT_EN, 1);
    }

    if (board_is_evm_sk(&header) || board_is_tq335x(&header))
        config_ddr(303, &ioregs_evmsk, &ddr3_data,
               &ddr3_cmd_ctrl_data, &ddr3_emif_reg_data, 0);
    else if (board_is_bone_lt(&header))
        config_ddr(400, &ioregs_bonelt,
               &ddr3_beagleblack_data,
               &ddr3_beagleblack_cmd_ctrl_data,
               &ddr3_beagleblack_emif_reg_data, 0);
    else if (board_is_evm_15_or_later(&header))
        config_ddr(303, &ioregs_evm15, &ddr3_evm_data,
               &ddr3_evm_cmd_ctrl_data, &ddr3_evm_emif_reg_data, 0);
    else
        config_ddr(266, &ioregs, &ddr2_data,
               &ddr2_cmd_ctrl_data, &ddr2_emif_reg_data, 0);
}

然后添加board_is_tq335x函数的具体实现，参考其它类似函数实现即可，由于我们的read_eeprom仅读到了name，其内容是"TQ335x"，故可如下实现，在board/ti/am335x/board.h中添加如下内容：

static inline int board_is_tq335x(struct am335x_baseboard_id *header)
{
    return !strncmp(header->name, "TQ335x", HDR_NAME_LEN);
}

最后是修改enable_board_pin_mux（board/ti/am335x/mux.c）函数，具体的修改内容如下：

void enable_board_pin_mux(struct am335x_baseboard_id *header)
{
    /* Do board-specific muxes. */
    if (board_is_bone(header) || board_is_tq335x(header)) {
        /* Beaglebone pinmux */
        configure_module_pin_mux(i2c1_pin_mux);
        configure_module_pin_mux(mii1_pin_mux);
        configure_module_pin_mux(mmc0_pin_mux);
#if defined(CONFIG_NAND)
        configure_module_pin_mux(nand_pin_mux);
#elif defined(CONFIG_NOR)
        configure_module_pin_mux(bone_norcape_pin_mux);
#else
        configure_module_pin_mux(mmc1_pin_mux);
#endif
    } else if (board_is_gp_evm(header)) {
        /* General Purpose EVM */
        unsigned short profile = detect_daughter_board_profile();
        configure_module_pin_mux(rgmii1_pin_mux);
        configure_module_pin_mux(mmc0_pin_mux);
        /* In profile #2 i2c1 and spi0 conflict. */
        if (profile & ~PROFILE_2)
            configure_module_pin_mux(i2c1_pin_mux);
        /* Profiles 2 & 3 don't have NAND */
#ifdef CONFIG_NAND
        if (profile & ~(PROFILE_2 | PROFILE_3))
            configure_module_pin_mux(nand_pin_mux);
#endif
        else if (profile == PROFILE_2) {
            configure_module_pin_mux(mmc1_pin_mux);
            configure_module_pin_mux(spi0_pin_mux);
        }
    } else if (board_is_idk(header)) {
        /* Industrial Motor Control (IDK) */
        configure_module_pin_mux(mii1_pin_mux);
        configure_module_pin_mux(mmc0_no_cd_pin_mux);
    } else if (board_is_evm_sk(header)) {
        /* Starter Kit EVM */
        configure_module_pin_mux(i2c1_pin_mux);
        configure_module_pin_mux(gpio0_7_pin_mux);
        configure_module_pin_mux(rgmii1_pin_mux);
        configure_module_pin_mux(mmc0_pin_mux_sk_evm);
    } else if (board_is_bone_lt(header)) {
        /* Beaglebone LT pinmux */
        configure_module_pin_mux(i2c1_pin_mux);
        configure_module_pin_mux(mii1_pin_mux);
        configure_module_pin_mux(mmc0_pin_mux);
#if defined(CONFIG_NAND)
        configure_module_pin_mux(nand_pin_mux);
#elif defined(CONFIG_NOR)
        configure_module_pin_mux(bone_norcape_pin_mux);
#else
        configure_module_pin_mux(mmc1_pin_mux);
#endif
    } else {
        puts("Unknown board, cannot configure pinmux.");
        hang();
    }
}

另外，这个版本的u-boot有个bug，需要修改fat_register_device（fs/fat/fat.c）函数：

int fat_register_device(block_dev_desc_t *dev_desc, int part_no)
{
    disk_partition_t info;

    /* First close any currently found FAT filesystem */
    cur_dev = NULL;

    /* Read the partition table, if present */
    if (get_partition_info(dev_desc, part_no, &info)) {
        /*if (part_no != 0) {
            printf("** Partition %d not valid on device %d **\n",
                    part_no, dev_desc->dev);
            return -1;
        }*/

        info.start = 0;
        info.size = dev_desc->lba;
        info.blksz = dev_desc->blksz;
        info.name[0] = 0;
        info.type[0] = 0;
        info.bootable = 0;
#ifdef CONFIG_PARTITION_UUIDS
        info.uuid[0] = 0;
#endif
    }

    return fat_set_blk_dev(dev_desc, &info);
}

至此，u-boot就已经可以启动了，但是有多余的步骤和log，不过可以去掉，修改file_fat_read_at（fs/fat/fat.c）函数：

long file_fat_read_at(const char *filename, unsigned long pos, void *buffer,
              unsigned long maxsize)
{
    debug("reading %s\n", filename);
    return do_fat_read_at(filename, pos, buffer, maxsize, LS_NO, 0);
}

最后，TQ335x是MLO启动u-boot，然后u-boot去启动内核，故可以去掉配置项CONFIG_SPL_OS_BOOT，具体的修改文件include/configs/ti_armv7_common.h：

#if defined(CONFIG_SPL_OS_BOOT_ENABLE)
#define CONFIG_SPL_OS_BOOT
#endif

至此，u-boot的移植工作就完成了，编译方法如下：

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- am335x_evm_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- -j8

其中，arm-linux-gnueabi-需要根据自己的交叉编译工具链前缀进行修改。完成u-boot的移植工作后我们来研究如何启动内核。

源码下载地址：

u-boot-2014.10 for TQ335x/TQ3358(SD卡启动)