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boot: remove informatnion about query_mca()

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as it was removed in the:

949163015c (diff-25ea8b4d2857dbd7b7ae86277dd464e8)

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pull/517/head
Alexander Kuleshov 7 years ago
parent 6543cf4994
commit 8d76549828
1 changed files with 4 additions and 69 deletions
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Booting/linux-bootstrap-2.md
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@ -401,13 +401,16 @@ Keyboard initialization
--------------------------------------------------------------------------------
The next step is the initialization of the keyboard with the call of the [`keyboard_init()`](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/main.c#L65) function. At first `keyboard_init` initializes registers using the `initregs` function and calling the [0x16](http://www.ctyme.com/intr/rb-1756.htm) interrupt for getting the keyboard status.
```c
initregs(&ireg);
ireg.ah = 0x02; /* Get keyboard status */
intcall(0x16, &ireg, &oreg);
boot_params.kbd_status = oreg.al;
```
After this it calls [0x16](http://www.ctyme.com/intr/rb-1757.htm) again to set repeat rate and delay.
```c
ireg.ax = 0x0305; /* Set keyboard repeat rate */
intcall(0x16, &ireg, NULL);
@ -418,75 +421,7 @@ Querying
The next couple of steps are queries for different parameters. We will not dive into details about these queries but will get back to it in later parts. Let's take a short look at these functions:
The [query_mca](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/mca.c#L18) routine calls the [0x15](http://www.ctyme.com/intr/rb-1594.htm) BIOS interrupt to get the machine model number, sub-model number, BIOS revision level, and other hardware-specific attributes:
```c
int query_mca(void)
{
struct biosregs ireg, oreg;
u16 len;
initregs(&ireg);
ireg.ah = 0xc0;
intcall(0x15, &ireg, &oreg);
if (oreg.eflags & X86_EFLAGS_CF)
return -1; /* No MCA present */
set_fs(oreg.es);
len = rdfs16(oreg.bx);
if (len > sizeof(boot_params.sys_desc_table))
len = sizeof(boot_params.sys_desc_table);
copy_from_fs(&boot_params.sys_desc_table, oreg.bx, len);
return 0;
}
```
It fills the `ah` register with `0xc0` and calls the `0x15` BIOS interruption. After the interrupt execution it checks the [carry flag](http://en.wikipedia.org/wiki/Carry_flag) and if it is set to 1, the BIOS doesn't support [**MCA**](https://en.wikipedia.org/wiki/Micro_Channel_architecture). If carry flag is set to 0, `ES:BX` will contain a pointer to the system information table, which looks like this:
```
Offset Size Description
00h WORD number of bytes following
02h BYTE model (see #00515)
03h BYTE submodel (see #00515)
04h BYTE BIOS revision: 0 for first release, 1 for 2nd, etc.
05h BYTE feature byte 1 (see #00510)
06h BYTE feature byte 2 (see #00511)
07h BYTE feature byte 3 (see #00512)
08h BYTE feature byte 4 (see #00513)
09h BYTE feature byte 5 (see #00514)
---AWARD BIOS---
0Ah N BYTEs AWARD copyright notice
---Phoenix BIOS---
0Ah BYTE ??? (00h)
0Bh BYTE major version
0Ch BYTE minor version (BCD)
0Dh 4 BYTEs ASCIZ string "PTL" (Phoenix Technologies Ltd)
---Quadram Quad386---
0Ah 17 BYTEs ASCII signature string "Quadram Quad386XT"
---Toshiba (Satellite Pro 435CDS at least)---
0Ah 7 BYTEs signature "TOSHIBA"
11h BYTE ??? (8h)
12h BYTE ??? (E7h) product ID??? (guess)
13h 3 BYTEs "JPN"
```
Next, we call the `set_fs` routine and pass the value of the `es` register to it. The implementation of `set_fs` is pretty simple:
```c
static inline void set_fs(u16 seg)
{
asm volatile("movw %0,%%fs" : : "rm" (seg));
}
```
This function contains inline assembly which gets the value of the `seg` parameter and puts it into the `fs` register. There are many functions in [boot.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/boot.h) like `set_fs`, for example `set_gs`, `fs`, `gs` for reading a value in it etc...
At the end of `query_mca` it just copies the table pointed to by `es:bx` to the `boot_params.sys_desc_table`.
The next step is getting [Intel SpeedStep](http://en.wikipedia.org/wiki/SpeedStep) information by calling the `query_ist` function. First of all, it checks the CPU level and if it is correct, calls `0x15` for getting info and saves the result to `boot_params`.
The first step is getting [Intel SpeedStep](http://en.wikipedia.org/wiki/SpeedStep) information by calling the `query_ist` function. First of all, it checks the CPU level and if it is correct, calls `0x15` for getting info and saves the result to `boot_params`.
The following [query_apm_bios](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/boot/apm.c#L21) function gets [Advanced Power Management](http://en.wikipedia.org/wiki/Advanced_Power_Management) information from the BIOS. `query_apm_bios` calls the `0x15` BIOS interruption too, but with `ah` = `0x53` to check `APM` installation. After the `0x15` execution, `query_apm_bios` functions check the `PM` signature (it must be `0x504d`), carry flag (it must be 0 if `APM` supported) and value of the `cx` register (if it's 0x02, protected mode interface is supported).

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