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Merge pull request #659 from changuoqiang/master

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Update linux-initialization-5.md
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Initialization/linux-initialization-5.md
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@ -165,7 +165,7 @@ The next step is initialization of early `ioremap`. In general there are two way
We already saw first method (`outb/inb` instructions) in the part about linux kernel booting [process](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-3.html). The second method is to map I/O physical addresses to virtual addresses. When a physical address is accessed by the CPU, it may refer to a portion of physical RAM which can be mapped on memory of the I/O device. So `ioremap` used to map device memory into kernel address space.
As i wrote above next function is the `early_ioremap_init` which re-maps I/O memory to kernel address space so it can access it. We need to initialize early ioremap for early initialization code which needs to temporarily map I/O or memory regions before the normal mapping functions like `ioremap` are available. Implementation of this function is in the [arch/x86/mm/ioremap.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/mm/ioremap.c). At the start of the `early_ioremap_init` we can see definition of the `pmd` point with `pmd_t` type (which presents page middle directory entry `typedef struct { pmdval_t pmd; } pmd_t;` where `pmdval_t` is `unsigned long`) and make a check that `fixmap` aligned in a correct way:
As i wrote above next function is the `early_ioremap_init` which re-maps I/O memory to kernel address space so it can access it. We need to initialize early ioremap for early initialization code which needs to temporarily map I/O or memory regions before the normal mapping functions like `ioremap` are available. Implementation of this function is in the [arch/x86/mm/ioremap.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/mm/ioremap.c). At the start of the `early_ioremap_init` we can see definition of the `pmd` pointer with `pmd_t` type (which presents page middle directory entry `typedef struct { pmdval_t pmd; } pmd_t;` where `pmdval_t` is `unsigned long`) and make a check that `fixmap` aligned in a correct way:
```C
pmd_t *pmd;
@ -354,7 +354,7 @@ struct x86_init_ops x86_init __initdata = {
}
```
As we can see here `memry_setup` field is `default_machine_specific_memory_setup` where we get the number of the [e820](http://en.wikipedia.org/wiki/E820) entries which we collected in the [boot time](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-2.html), sanitize the BIOS e820 map and fill `e820map` structure with the memory regions. As all regions are collected, print of all regions with printk. You can find this print if you execute `dmesg` command and you can see something like this:
As we can see here `memory_setup` field is `default_machine_specific_memory_setup` where we get the number of the [e820](http://en.wikipedia.org/wiki/E820) entries which we collected in the [boot time](https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-2.html), sanitize the BIOS e820 map and fill `e820map` structure with the memory regions. As all regions are collected, print of all regions with printk. You can find this print if you execute `dmesg` command and you can see something like this:
```
[ 0.000000] e820: BIOS-provided physical RAM map: