; Arguments:
;       ah              Bus Number          (0 .. 255)
;       al              Device Number       (0 .. 31)
;
; Returns:
;   - true/false (eax)
pci_device_exists:
    push        dword esi
    sub         esp,                    8
    mov         esi,                    esp

    mov         [esi],                  edx
    mov         [esi + 4],              eax

.make_address:
    xor         eax,                    eax
    ; Enable Bit
    or          al,                     1
    ; Make space for 8 Reserved Bits and 8 Bytes of bus number.
    shl         eax,                    15
    ; Bus Number
    mov         al,                     [esi + 5]
    ; Device Number
    ; Make space for device number
    shl         eax,                    5
    mov         dl,                     [esi + 4]
    and         dl,                     0x1f
    or          al,                     dl
    shl         eax,                    11

.input_output:
    mov         dx,                     PCI_CONFIG_ADDRESS_PORT
    out         dx,                     eax

    mov         dx,                     PCI_CONFIG_DATA_PORT
    in          eax,                    dx

    cmp         ax,                     0xffff
    jne         .device_found

.not_a_device:
    mov         edx,                    [esi]

    add         esp,                    8
    pop         dword esi

    xor         eax,                    eax
    ret
.device_found:
    mov         edx,                    [esi]

    add         esp,                    8
    pop         dword esi
    mov         eax,                    1
    ret



; Arguments:
;   [FURTHEST FROM EBP]
;     3. U16            PCI Device Class & Subclass
;                       (Higher byte: Class, lower byte: Subclass)
;     2. U16            PCI Device Address
;                       (Higher byte: Bus Address,
;                       lower byte:  Device Address)
;     1. Ptr32          Pointer to PCI driver area of 65536 bytes
;   [NEAREST TO EBP]
pci_append_device:
    push        dword esi
    sub         esp,                    64
    mov         esi,                    esp

    mov         [esi + (64 - 4)],       eax
    mov         [esi + (64 - 8)],       ebx
    mov         [esi + (64 - 12)],      ecx
    mov         [esi + (64 - 20)],      edi

.get_device_count:
    mov         ebx,                    [ebp - 4]
    xor         ecx,                    ecx
    mov         cx,                     [ebx + PCI_DEVICE_COUNT_OFFSET]
    mov         [esi + 4],              cx

.calculate_device_offset:
    ; Every device slot has 16 bytes, multiply index with 16
    shl         ecx,                    4
    ; Point into driver device area (add device area start on top)
    mov         ebx,                    [ebp - 4]
    add         ebx,                    PCI_DEVICE_AREA_OFFSET
    add         ebx,                    ecx

.set_device:
    mov         cx,                     [ebp - 6]
    mov         [ebx],                  cx
    mov         cx,                     [ebp - 8]
    mov         [ebx + 2],              cx

.increment_device_count:
    mov         ebx, [ebp - 4]
    inc         word [ebx + PCI_DEVICE_COUNT_OFFSET]

.epilog:
    mov         eax,                    [esi + (64 - 4)]
    mov         ebx,                    [esi + (64 - 8)]
    mov         ecx,                    [esi + (64 - 12)]
    mov         edi,                    [esi + (64 - 20)]

    add         esp,                    64
    pop         dword                   esi
    ret



; Arguments:
;   [FURTHER FROM EBP]
;     2.  U16           Device Number
;     1.  U16           Bus Number
;   [NEAREST TO EBP]
;
; Returns:
;       ax             PCI Device Class & Subclass
;                      (Higher byte: Class, lower byte: Subclass)
pci_get_device_class_at_address:
    push        dword                   esi
    sub         esp,                    64
    mov         esi,                    esp

    mov         [esi + (64 - 8)],       ebx
    mov         [esi + (64 - 12)],      ecx
    mov         [esi + (64 - 16)],      edx
    mov         [esi + (64 - 20)],      edi

.create_address:
    xor         eax,                    eax
    ; Enable Bit
    or          al,                     1
    ; Make space for 8 Reserved Bits and 8 Bytes of bus number.
    shl         eax,                    15
    ; Bus Number
    mov         al,                     [ebp - 2]
    ; Device Number
    ; Make space for device number
    shl         eax,                    5
    mov         dl,                     [ebp - 4]
    and         dl,                     0x1f
    or          al,                     dl
    shl         eax,                    11

    ; Include the register offset of the configuration space
    ; register which contains the class and subclass
    or          eax,                    8

.input_output:

    mov         dx,                     PCI_CONFIG_ADDRESS_PORT
    out         dx,                     eax

    mov         dx,                     PCI_CONFIG_DATA_PORT
    in          eax,                    dx

    ; Remove the parts of the register which aren't part of the
    ; PCI class- and subclass-code
    shr         eax,                    16

.epilog:
    mov         ebx,                    [esi + (64 - 8)]
    mov         ecx,                    [esi + (64 - 12)]
    mov         edx,                    [esi + (64 - 16)]
    mov         edi,                    [esi + (64 - 20)]

    add         esp,                    64
    pop         dword esi
    ret



; Arguments:
;   [FURTHER FROM EBP]
;     2. U32            Bus Number          (0 .. 255)
;     1. Ptr32          Pointer to PCI driver area of 65536 bytes
;   [NEAREST TO EBP]
;
; Returns:
;   - Number of devics on the bus (eax)
pci_enumerate_bus:
    push        dword esi
    sub         esp,                    64
    mov         esi,                    esp

    mov         [esi + (64 - 8)],       ebx
    mov         [esi + (64 - 12)],      ecx
    mov         [esi + (64 - 16)],      edx
    mov         [esi + (64 - 20)],      edi
    ; [esi]:        Device-in-bus Index
    ; [esi + 4]:    Number of existing devices
    ; [esi + 8]:    Bus number
    ; [esi + 12]:   PCI driver area pointer
    mov         [esi],                  dword 0
    mov         [esi + 4],              dword 0
    mov         eax,                    [ebp - 8]
    mov         [esi + 8],              eax
    mov         eax,                    [ebp - 4]
    mov         [esi + 12],             eax
.initialize_device_loop:

.device_loop:
    cmp         [esi],                  dword 32
    jae         .epilog

.test_whether_device_exists:
    mov         ah,                     [esi + 8]   ; Bus Number 
    mov         al,                     [esi]       ; Device Number
    mov         [esi + 16],             ax

    push        ebp
    mov         ebp,                    esp
    call        pci_device_exists
    mov         esp,                    ebp
    pop         ebp

    cmp         ax,                     0
    je          .no_device

.append_device:
    mov         al,                     [esi + 8]
    mov         ah,                     [esi]

    ; Device Number in DX
    xor         dx,                     dx
    mov         dl,                     ah
    xor         ah,                     ah

    push        ebp
    mov         ebp,                    esp
    push        ax
    push        dx
    call        pci_get_device_class_at_address
    mov         esp,                    ebp
    pop         ebp

    mov         cx,                     ax
    mov         ax,                     [esi + 16]

    push        ebp
    mov         ebp,                    esp
    push        dword [esi + 12]
    push        ax
    push        cx
    call        pci_append_device
    mov         esp, ebp
    pop         ebp

    mov         ebx,                    [ebp - 4]

.no_device:
    inc         dword [esi]
    jmp         .device_loop

.epilog:
    mov         ebx,                    [esi + (64 - 8)]
    mov         ecx,                    [esi + (64 - 12)]
    mov         edx,                    [esi + (64 - 16)]
    mov         edi,                    [esi + (64 - 20)]

    mov         eax,                    [esi + 4]

    add         esp,                    64
    pop         dword esi
    ret



; Arguments:
;   [FURTHEST FROM EBP]
;     2. U32            Maximum number of devices to enumerate
;                       (0 to eliminate limit)
;     1. Ptr32          Pointer to PCI driver area of 65536 bytes
;   [NEAREST TO EBP]
; Returns:
;     eax:              Number of devices read
pci_enumerate:
    push        dword esi
    sub         esp,                    64
    mov         esi,                    esp

    mov         [esi + (64 - 4)],       eax
    mov         [esi + (64 - 8)],       ebx
    mov         [esi + (64 - 12)],      ecx
    mov         [esi + (64 - 16)],      edx
    mov         [esi + (64 - 20)],      edi

    ; [esi]:    Number of devices found
    ; ecx:      Bus Index

    mov         edx,                    [ebp - 4]
    mov         [esi + 4],              edx

    ; Set the device count to 0 explicitly, just for safety.
    mov         ebx,                    [ebp - 4]
    add         ebx,                    PCI_DEVICE_COUNT_OFFSET
    mov         [ebx],                  word 0

.bus_loop:
    xor         ecx,                    ecx
    mov         [esi],                  dword 0

.bus_loop_body:
    ; Test whether the device count is unlimited,
    ; ignore the device count check if it is.
    cmp         [ebp - 8],              dword 0
    je          .call_bus_enumerator

    mov         edx,                    [esi]
    cmp         edx,                    [ebp - 8]
    jae         .epilog

.call_bus_enumerator:
    push        ebp
    mov         ebp,                    esp
    push        dword [esi + 4]
    push        ecx
    call        pci_enumerate_bus
    mov         esp,                    ebp
    pop         ebp

    ; Add the number of devices found on the bus
    ; to the number of devices found in total.
    add         [esi],                  eax
    mov         ebx,                    [esi + 4]
    add         [ebx + PCI_DEVICE_COUNT_OFFSET], ax

    ; Go to the next bus (if there is one)
    inc         ecx
    cmp         ecx,                    256
    jb          .bus_loop_body

.epilog:
    mov         ebx,                    [esi + (64 - 8)]
    mov         ecx,                    [esi + (64 - 12)]
    mov         edx,                    [esi + (64 - 16)]
    mov         edi,                    [esi + (64 - 20)]
    mov         eax,                    [esi]

    add         esp,                    64
    pop         dword esi
    ret