Linux MTD子系统学习（三）

淩亂°似流年 2022-01-09 10:01 537阅读 0赞

# Linux MTD子系统学习（三） #

## 4 Linux mtd分区的建立 ##

### 4.1 mtd分区的建立方法 ###

#### 4.1.1 内核添加 ####

在内核中添加分区表是就内核常用的方法，主要是在平台设备中添加mtd\_parttion，如下：

struct mtd_partition m25p80_part[] = {
        	{
            		.name       = "Bootloader",
            		.offset     = 0,
            		.size       = (1 * SZ_1M),
            		.mask_flags = MTD_CAP_NANDFLASH,
        	},
        	{
            		.name       = "Kernel",
            		.offset     = (1 * SZ_1M),
            		.size       = (31 * SZ_1M) ,
            		.mask_flags = MTD_CAP_NANDFLASH,
        	},
        	{
            		.name       = "User",
            		.offset     = (32 * SZ_1M),
            		.size       = (16 * SZ_1M) ,
        	},
        	{
           	 	.name       = "File System",
            		.offset     = (48 * SZ_1M),
            		.size       = (96 * SZ_1M),
        	}
    };
    
    static struct flash_platform_data m25p80_platform_data[] = {
        [0] = {
            .name       = "m25p80",
            .nr_parts  = ARRAY_SIZE(m25p80_part),
            .parts = m25p80_part,
        },
    };
    
    static struct spi_board_info xxx_spi_nor_device[] = {
    	{
             .modalias = "m25p80",	//spi设备名字，设备驱动探测时会用到该项
              .max_speed_hz = 25000000,      
              .bus_num = 1,
             .chip_select = 1,//该spi设备的片选编号
              .mode = SPI_MODE_0,	//此spi设备支持spi总线的工作模式
             .platform_data = &m25p80_platform_data, //存放flash分区表
    	},
    	{},
    };

#### 4.1.2 bootargs传参 ####

在u-boot或device\_tree可以通过添加mtdparts信息到bootargs中，u-boot启动后会将bootargs中的信息传送给kernel,，kernel在启动的时候会解析bootargs中mtdparts的部分，这边举个例子：

mtdparts=spi0.0:128k(boot)ro,128k(dtb)ro,9984k(kernel)ro,3M(rootfs)ro,-(data)

为了使kernel能够解析mtdparts信息，我们需要将内核中的**Device Drivers -> Memory Technology Device (MTD) support ->Command line partition table parsing**选项开启。

#### 4.1.3 dts传参 ####

dts传参的原理其实和u-boot一样，区别在于：u-boot的时候是通过cmdlinepart.c文件实现分区信息写入LIST\_HEAD(mtd\_partitions)链表，dts则是用过ofpart.c文件实现分区信息写入LIST\_HEAD mtd\_partitions)链表，所以同样要把ofpart.c文件的宏打开，在调用mtd\_device\_parse\_register(mtd, probe\_types,&ppdata, NULL, 0);函数的时候types要设置成ofpart。  
具体参考例子，如下：

&spi0 {
    	status = "okay";
    	pinctrl-names = "default";
    	pinctrl-0 = <&spi0_0>;
    	num-cs = <1>;    
    	ranges = <0 0x08000000>;
        nor_flash@0 {
            partition@1 {
                label = "Bootloader";
                reg = <0x00000000 0x00010000>;
            };
            partition@2 {
                label = "Kernel";
                reg = <0x00100000 0x002000000>;
            };
            partition@3 {
                label = "User";
                reg = <0x002000000 0x03000000>;
            };
            partition@4 {
                label = "File System";
                reg = <0x03000000 0x08000000>;
            };
        };
    };

### 4.2 mtd分区处理流程 ###

#### 4.2.1 mtd分区解析 ####

##### 4.2.1.1 parse\_mtd\_partitions #####

该函数依据分区表的类型（以上三种），找到对应的解析方法，解析相关的分区信息，建立kernel可识别的分区表格式，用于后面添加分区表。  
源码：drivers/mtd/mtdpart.c

int parse_mtd_partitions(struct mtd_info *master, const char *const *types,
    			 struct mtd_partitions *pparts,
    			 struct mtd_part_parser_data *data)
    {
    	struct mtd_part_parser *parser;
    	int ret, err = 0;
    
    //判断当前分区表信息的类型，内核添加方法则无需使用默认
    	if (!types) 
    		types = default_mtd_part_types;//见后面
    
    	for ( ; *types; types++) {
    		pr_debug("%s: parsing partitions %s\n", master->name, *types);
    		parser = mtd_part_parser_get(*types);//获取解析方法
    		if (!parser && !request_module("%s", *types))
    			parser = mtd_part_parser_get(*types);
    		pr_debug("%s: got parser %s\n", master->name,
    			 parser ? parser->name : NULL);
    		if (!parser)
    			continue;
    		ret = mtd_part_do_parse(parser, master, pparts, data);//解析分区表
    		/* Found partitions! */
    		if (ret > 0)
    			return 0;
    		mtd_part_parser_put(parser);//解析异常，释放分区表
    		/*
    		 * Stash the first error we see; only report it if no parser
    		 * succeeds
    		 */
    		if (ret < 0 && !err)
    			err = ret;
    	}
    	return err;
    }
    
    //一般只定义了两种类型
    static const char * const default_mtd_part_types[] = {
    	"cmdlinepart",
    	"ofpart",
    	NULL
    };

##### 4.2.1.2 mtd\_part\_do\_parse #####

该函数将回调具体的解析函数解析分区表。  
源码：drivers/mtd/mtdpart.c

static int mtd_part_do_parse(struct mtd_part_parser *parser,
        			     struct mtd_info *master,
        			     struct mtd_partitions *pparts,
        			     struct mtd_part_parser_data *data)
        {
        	int ret;
    	    //回调解析方法中的解析函数解析分区信息，建立分区表
    		ret = (*parser->parse_fn)(master, &pparts->parts, data);
    		pr_debug("%s: parser %s: %i\n", master->name, parser->name, ret);
    		if (ret <= 0)//解析异常判断
    			return ret;
    	
    		pr_notice("%d %s partitions found on MTD device %s\n", ret,
    			  parser->name, master->name);
    	
    		pparts->nr_parts = ret;//分区数目
    		pparts->parser = parser;
    	
    		return ret;
    	}

#### 4.2.2 mtd分区解析方法注册 ####

该部分调用register\_mtd\_parser()，其为宏函数，定义如下：

#define register_mtd_parser(parser) __register_mtd_parser(parser, THIS_MODULE)

通过该函数，将相关的解析方法添加到part\_parsers链表中，如下：

int __register_mtd_parser(struct mtd_part_parser *p, struct module *owner)
    {
    	p->owner = owner;
    
    	if (!p->cleanup)
    		p->cleanup = &mtd_part_parser_cleanup_default;
    
    	spin_lock(&part_parser_lock);
    	list_add(&p->list, &part_parsers);
    	spin_unlock(&part_parser_lock);
    
    	return 0;
    }

##### 4.2.2.1 cmdline\_parser #####

源码：drivers/mtd/cmdlinepart.c

static struct mtd_part_parser cmdline_parser = {
    	.parse_fn = parse_cmdline_partitions,//解析方法的实现，具体请查看源码
    	.name = "cmdlinepart",
    };
    
    static int __init cmdline_parser_init(void)
    {
    	if (mtdparts)
    		mtdpart_setup(mtdparts);
    	register_mtd_parser(&cmdline_parser);//注册解析方法
    	return 0;
    }
    
    static void __exit cmdline_parser_exit(void)
    {
    	deregister_mtd_parser(&cmdline_parser);
    }
    
    module_init(cmdline_parser_init);
    module_exit(cmdline_parser_exit);

##### 4.2.2.2 ofpart\_parser #####

此处注册了两种设备树的解析方法，差别在设备树中两种的格式不一致。  
源码：drivers/mtd/ofpart.c

static struct mtd_part_parser ofpart_parser = {
    	.parse_fn = parse_ofpart_partitions,
    	.name = "ofpart",
    };
    
    static struct mtd_part_parser ofoldpart_parser = {
    	.parse_fn = parse_ofoldpart_partitions,
    	.name = "ofoldpart",
    };
    
    static int __init ofpart_parser_init(void)
    {
    	register_mtd_parser(&ofpart_parser);
    	register_mtd_parser(&ofoldpart_parser);
    	return 0;
    }
    
    static void __exit ofpart_parser_exit(void)
    {
    	deregister_mtd_parser(&ofpart_parser);
    	deregister_mtd_parser(&ofoldpart_parser);
    }
    
    module_init(ofpart_parser_init);
    module_exit(ofpart_parser_exit);

#### 4.2.3 mtd分区添加 ####

##### 4.2.3.1 mtd\_add\_device\_partitions #####

源码：drivers/mtd/mtdcore.c

static int mtd_add_device_partitions(struct mtd_info *mtd,
    				     struct mtd_partitions *parts)
    {
    	const struct mtd_partition *real_parts = parts->parts;
    	int nbparts = parts->nr_parts;
    	int ret;
    
        //分区数目为0，建立分区的mtd_info，添加mtd设备，建立一个分区
    	if (nbparts == 0 || IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER)) {
    		ret = add_mtd_device(mtd);
    		if (ret)
    			return ret;
    	}
    
    	if (nbparts > 0) {//分区数目大于0，建立分区的mtd_info，再添加mtd设备
    		ret = add_mtd_partitions(mtd, real_parts, nbparts);
    		if (ret && IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
    			del_mtd_device(mtd);
    		return ret;
    	}
    
    	return 0;
    }

##### 4.2.3.2 add\_mtd\_partitions #####

源码：drivers/mtd/mtdcore.c

int add_mtd_partitions(struct mtd_info *master,
    		       const struct mtd_partition *parts,
    		       int nbparts)
    {
    	struct mtd_part *slave;
    	uint64_t cur_offset = 0;
    	int i;
    
    	printk(KERN_NOTICE "Creating %d MTD partitions on \"%s\":\n", nbparts, master->name);
    
    	for (i = 0; i < nbparts; i++) {
            //建立当前分区信息，初始化slave->mtd
    		slave = allocate_partition(master, parts + i, i, cur_offset); 
    		if (IS_ERR(slave)) {
    			del_mtd_partitions(master);
    			return PTR_ERR(slave);
    		}
    
    		mutex_lock(&mtd_partitions_mutex);
    		list_add(&slave->list, &mtd_partitions);//添加分区到分区链表中
    		mutex_unlock(&mtd_partitions_mutex);
    
    		add_mtd_device(&slave->mtd);//添加当前分区为mtd设备
    		mtd_add_partition_attrs(slave);
    		if (parts[i].types)//判断当前分区是否再建立子分区
    			mtd_parse_part(slave, parts[i].types);
    
    		cur_offset = slave->offset + slave->mtd.size;
    	}
    
    	return 0;
    }

##### 4.2.3.3 add\_mtd\_device #####

源码：drivers/mtd/mtdcore.c

int add_mtd_device(struct mtd_info *mtd)
    {
    	struct mtd_notifier *not;
    	int i, error;
    
    	/*
    	 * May occur, for instance, on buggy drivers which call
    	 * mtd_device_parse_register() multiple times on the same master MTD,
    	 * especially with CONFIG_MTD_PARTITIONED_MASTER=y.
    	 */
    	if (WARN_ONCE(mtd->dev.type, "MTD already registered\n"))
    		return -EEXIST;
    
    	BUG_ON(mtd->writesize == 0);
    	mutex_lock(&mtd_table_mutex);
    
    	i = idr_alloc(&mtd_idr, mtd, 0, 0, GFP_KERNEL);
    	if (i < 0) {
    		error = i;
    		goto fail_locked;
    	}
    
    	mtd->index = i;
    	mtd->usecount = 0;
    
    	/* default value if not set by driver */
    	if (mtd->bitflip_threshold == 0)
    		mtd->bitflip_threshold = mtd->ecc_strength;
    
    	if (is_power_of_2(mtd->erasesize))
    		mtd->erasesize_shift = ffs(mtd->erasesize) - 1;
    	else
    		mtd->erasesize_shift = 0;
    
    	if (is_power_of_2(mtd->writesize))
    		mtd->writesize_shift = ffs(mtd->writesize) - 1;
    	else
    		mtd->writesize_shift = 0;
    
    	mtd->erasesize_mask = (1 << mtd->erasesize_shift) - 1;
    	mtd->writesize_mask = (1 << mtd->writesize_shift) - 1;
    
    	/* Some chips always power up locked. Unlock them now */
    	if ((mtd->flags & MTD_WRITEABLE) && (mtd->flags & MTD_POWERUP_LOCK)) {
    		error = mtd_unlock(mtd, 0, mtd->size);
    		if (error && error != -EOPNOTSUPP)
    			printk(KERN_WARNING
    			       "%s: unlock failed, writes may not work\n",
    			       mtd->name);
    		/* Ignore unlock failures? */
    		error = 0;
    	}
    
    	/* Caller should have set dev.parent to match the
    	 * physical device, if appropriate.
    	 */
    	mtd->dev.type = &mtd_devtype;
    	mtd->dev.class = &mtd_class;
    	mtd->dev.devt = MTD_DEVT(i);//可读写的字符设备的次设备号为偶数
    	dev_set_name(&mtd->dev, "mtd%d", i);//设置字符设备名
    	dev_set_drvdata(&mtd->dev, mtd);    //设置设备私有数据
    	of_node_get(mtd_get_of_node(mtd));
    	error = device_register(&mtd->dev);  //注册可读写的字符设备
    	if (error)
    		goto fail_added;
    
    	if (!IS_ERR_OR_NULL(dfs_dir_mtd)) {
    		mtd->dbg.dfs_dir = debugfs_create_dir(dev_name(&mtd->dev), dfs_dir_mtd);
    		if (IS_ERR_OR_NULL(mtd->dbg.dfs_dir)) {
    			pr_debug("mtd device %s won't show data in debugfs\n",
    				 dev_name(&mtd->dev));
    		}
    	}
        //创建只读的字符设备，次设备号为奇数
    	device_create(&mtd_class, mtd->dev.parent, MTD_DEVT(i) + 1, NULL,
    		      "mtd%dro", i);
    
    	pr_debug("mtd: Giving out device %d to %s\n", i, mtd->name);
    	/* No need to get a refcount on the module containing
    	   the notifier, since we hold the mtd_table_mutex */
        //查找mtd_notifiers链表中合适的mtd设备类型，添加mtd设备
    	list_for_each_entry(not, &mtd_notifiers, list)
    		not->add(mtd);
    
    	mutex_unlock(&mtd_table_mutex);
    	/* We _know_ we aren't being removed, because
    	   our caller is still holding us here. So none
    	   of this try_ nonsense, and no bitching about it
    	   either. :) */
    	__module_get(THIS_MODULE);
    	return 0;
    
    fail_added:
    	of_node_put(mtd_get_of_node(mtd));
    	idr_remove(&mtd_idr, i);
    fail_locked:
    	mutex_unlock(&mtd_table_mutex);
    	return error;
    }