【转】（DT系列六）devicetree中数据和 struct device有什么关系

原文网址：http://www.cnblogs.com/biglucky/p/4057499.html

devicetree中数据和structdevice有什么关系

总体来说，devicetree与structdevice的关系应该还是在其生成platformdevice的时候，一直传递的structdevice *parent参数。下面先把其源码中传递过程描述如下（仍以At91rm9200为例）：

1,

DT_MACHINE_START(at91sam_dt,"Atmel AT91SAM (Device Tree)")

/*Maintainer: Atmel */

.timer =&at91sam926x_timer,

.map_io =at91_map_io,

.init_early =at91_dt_initialize,

.init_irq =at91_dt_init_irq,

.init_machine =at91_dt_device_init,

.dt_compat =at91_dt_board_compat,

MACHINE_END

2,

staticvoid __init at91_dt_device_init(void)

{

of_platform_populate(NULL,of_default_bus_match_table, NULL, NULL);

}

3,

/**

*of_platform_populate() - Populate platform_devices from device treedata

*@root: parent of the first level to probe or NULL for the root of thetree

*@matches: match table, NULL to use the default

*@parent: parent to hook devicesfrom, NULL for toplevel

*

*Similar to of_platform_bus_probe(), this function walks the devicetree

*and creates devices from nodes. It differs in that it follows themodern

*convention of requiring all device nodes to have a 'compatible'property,

*and it is suitable for creating devices which are children of theroot

*node (of_platform_bus_probe will only create children of the rootwhich

*are selected by the @matches argument).

*

*New board support should be using this function instead of

*of_platform_bus_probe().

*

*Returns 0 on success, < 0 on failure.

*/

//从devicetree数据中populateplatform devices。

intof_platform_populate(structdevice_node *root,

conststruct of_device_id *matches,

conststruct of_dev_auxdata *lookup,

structdevice *parent)

{

structdevice_node *child;

intrc = 0;

root= root ? of_node_get(root) : of_find_node_by_path("/");

if(!root)

return-EINVAL;

for_each_child_of_node(root,child) {

//生成platformdevice

rc= of_platform_bus_create(child,matches, lookup, parent,true);

if(rc)

break;

}

of_node_put(root);

returnrc;

}

4,

/**

*of_platform_bus_create() - Create a device for a node and itschildren.

*@bus: device node of the bus to instantiate

*@matches: match table for bus nodes

*@lookup: auxdata table for matching id and platform_data with devicenodes

*@parent: parent for new device, or NULL for top level.

*@strict: require compatible property

*

*Creates a platform_device for the provided device_node, andoptionally

*recursively create devices for all the child nodes.

*/

//为节点和其孩子节点生成一个设备文件。

staticint of_platform_bus_create(structdevice_node *bus,

const struct of_device_id *matches,

const struct of_dev_auxdata *lookup,

struct device *parent, boolstrict)

{

conststruct of_dev_auxdata *auxdata;

structdevice_node *child;

structplatform_device *dev;

constchar *bus_id = NULL;

void*platform_data = NULL;

intrc = 0;

/*Make sure it has a compatible property */

if(strict && (!of_get_property(bus, "compatible",NULL))) {

pr_debug("%s()- skipping %s, no compatible prop\n",

__func__, bus->full_name);

return0;

}

auxdata= of_dev_lookup(lookup, bus);

if(auxdata) {

bus_id= auxdata->name;

platform_data= auxdata->platform_data;

}

if(of_device_is_compatible(bus, "arm,primecell")) {

of_amba_device_create(bus,bus_id, platform_data, parent);

return0;

}

dev= of_platform_device_create_pdata(bus,bus_id, platform_data, parent);

if(!dev || !of_match_node(matches, bus))

return0;

for_each_child_of_node(bus,child) {

pr_debug(" create child: %s\n", child->full_name);

rc= of_platform_bus_create(child, matches, lookup, &dev->dev,strict);

if(rc) {

of_node_put(child);

break;

}

}

returnrc;

}

代码在这儿分了两步走：4.1和4.2。

4.1

staticstruct amba_device *of_amba_device_create(structdevice_node *node,

const char *bus_id,

void *platform_data,

struct device *parent)

{

structamba_device *dev;

constvoid *prop;

inti, ret;

pr_debug("Creatingamba device %s\n", node->full_name);

if(!of_device_is_available(node))

returnNULL;

dev= amba_device_alloc(NULL, 0, 0);

if(!dev)

returnNULL;

/*setup generic device info */

dev->dev.coherent_dma_mask= ~0;

dev->dev.of_node= of_node_get(node);

dev->dev.parent= parent;

dev->dev.platform_data= platform_data;

…...

}

4.2

/**

*of_platform_device_create_pdata - Alloc, initialize and register anof_device

*@np: pointer to node to create device for

*@bus_id: name to assign device

*@platform_data: pointer to populate platform_data pointer with

*@parent: Linux device model parentdevice.

*

*Returns pointer to created platform device, or NULL if a device wasnot

*registered. Unavailable devices will not get registered.

*/

//分配内存，初始化和注册一个of_device

structplatform_device *of_platform_device_create_pdata(

structdevice_node *np,

constchar *bus_id,

void*platform_data,

structdevice *parent)

{

structplatform_device *dev;

if(!of_device_is_available(np))

returnNULL;

dev= of_device_alloc(np,bus_id, parent);

…...

returndev;

}

4.2.1

/**

*of_device_alloc - Allocate and initialize an of_device

*@np: device node to assign to device

*@bus_id: Name to assign to the device. May be null to use defaultname.

*@parent: Parent device.

*/

//分配内存和初始化of_device

structplatform_device *of_device_alloc(structdevice_node *np,

const char *bus_id,

struct device *parent)

{

structplatform_device *dev;

intrc, i, num_reg = 0, num_irq;

structresource *res, temp_res;

dev= platform_device_alloc("", -1);

if(!dev)

returnNULL;

/*count the io and irq resources */

if(of_can_translate_address(np))

while(of_address_to_resource(np, num_reg, &temp_res) == 0)

num_reg++;

num_irq= of_irq_count(np);

/*Populate the resource table */

if(num_irq || num_reg) {

res= kzalloc(sizeof(*res) * (num_irq + num_reg), GFP_KERNEL);

if(!res) {

platform_device_put(dev);

returnNULL;

}

dev->num_resources= num_reg + num_irq;

dev->resource= res;

for(i = 0; i < num_reg; i++, res++) {

rc= of_address_to_resource(np, i, res);

WARN_ON(rc);

}

WARN_ON(of_irq_to_resource_table(np,res, num_irq) != num_irq);

}

dev->dev.of_node= of_node_get(np);

#ifdefined(CONFIG_MICROBLAZE)

dev->dev.dma_mask= &dev->archdata.dma_mask;

#endif

dev->dev.parent= parent;

if(bus_id)

dev_set_name(&dev->dev,"%s", bus_id);

else

of_device_make_bus_id(&dev->dev);

returndev;

}

总的分析：parent参数开始初始化为NULL，其中一直没有赋值，直到最后赋值给platformdevice的dev.parent属性。其中关系耐人寻味。