SPEAr PCIe Gadget Driver

저자·source·지원 chip

SPEAr PCIe Gadget driver의 저자는 Pratyush Anand <pratyush.anand@gmail.com>입니다. 원문에 표시된 source 위치는 `driver/misc/spear13xx_pcie_gadget.c`이며 SPEAr1300과 SPEAr1310을 지원합니다.

Menuconfig에서는 `Device Drivers` → `Misc devices` → `PCIe gadget support for SPEAr13XX platform` 경로로 선택합니다.

.. SPDX-License-Identifier: GPL-2.0

========================
Spear PCIe Gadget Driver
========================

Author
======
Pratyush Anand (pratyush.anand@gmail.com)

Location
========
driver/misc/spear13xx_pcie_gadget.c

Supported Chip:
===============
SPEAr1300
SPEAr1310

Menuconfig option:
==================
Device Drivers
        Misc devices
                PCIe gadget support for SPEAr13XX platform

Driver 목적

이 driver는 configfs interface로 읽고 쓸 수 있는 여러 node를 제공합니다. 선택한 dual-mode PCIe controller를 device mode로 구성한 뒤 여러 register를 programming해 특정 device type으로 만드는 것이 주 목적입니다. 이를 통해 SPEAr의 PCIe device capability를 보여줄 수 있습니다.

purpose
=======
This driver has several nodes which can be read/written by configfs interface.
Its main purpose is to configure selected dual mode PCIe controller as device
and then program its various registers to configure it as a particular device
type. This driver can be used to show spear's PCIe device capability.

Node 읽기 동작

Description of different nodes:
===============================

read behavior of nodes:
-----------------------

=============== ==============================================================
link                 gives ltssm status.
int_type         type of supported interrupt
no_of_msi         zero if MSI is not enabled by host. A positive value is the
                number of MSI vector granted.
vendor_id        returns programmed vendor id (hex)
device_id        returns programmed device id(hex)
bar0_size:        returns size of bar0 in hex.
bar0_address        returns address of bar0 mapped area in hex.
bar0_rw_offset        returns offset of bar0 for which bar0_data will return value.
bar0_data        returns data at bar0_rw_offset.
=============== ==============================================================

Node 쓰기 동작

Kernel이 alignment를 위해 BAR size와 address를 변경할 수 있으므로 `bar0_address`를 쓴 뒤 size와 address를 다시 읽어 확인해야 합니다.

write behavior of nodes:
------------------------

=============== ================================================================
link                 write UP to enable ltsmm DOWN to disable
int_type        write interrupt type to be configured and (int_type could be
                INTA, MSI or NO_INT). Select MSI only when you have programmed
                no_of_msi node.
no_of_msi        number of MSI vector needed.
inta                write 1 to assert INTA and 0 to de-assert.
send_msi        write MSI vector to be sent.
vendor_id        write vendor id(hex) to be programmed.
device_id        write device id(hex) to be programmed.
bar0_size        write size of bar0 in hex. default bar0 size is 1000 (hex)
                bytes.
bar0_address        write        address of bar0 mapped area in hex. (default mapping of
                bar0 is SYSRAM1(E0800000). Always program bar size before bar
                address. Kernel might modify bar size and address for alignment,
                so read back bar size and address after writing to cross check.
bar0_rw_offset        write offset of bar0 for which        bar0_data will write value.
bar0_data        write data to be written at bar0_rw_offset.
=============== ================================================================

1MB RAM endpoint 구성

예제는 PCIe host가 gadget을 1MB RAM으로 보도록 register를 programming합니다. 먼저 configfs를 `/Config`에 mount하고 n번째 controller의 `/config/pcie_gadget.n/`으로 이동합니다.

# mount -t configfs none /Config
# cd /config/pcie_gadget.n/
# echo 104A >> vendor_id
# echo CD80 >> device_id
# echo 100000 >> bar0_size
# cat bar0_size

BAR0 address에는 host에 보이게 할 memory의 physical address를 씁니다. 예제는 DDR `0x2100000`을 사용합니다. 다른 peripheral의 base address도 노출할 수 있으며, UART base를 쓰면 host에서 UART로 보입니다.

# echo 2100000 >> bar0_address

Node programming example
========================

Program all PCIe registers in such a way that when this device is connected
to the PCIe host, then host sees this device as 1MB RAM.

::

    #mount -t configfs none /Config

For nth PCIe Device Controller::

    # cd /config/pcie_gadget.n/

Now you have all the nodes in this directory.
program vendor id as 0x104a::

    # echo 104A >> vendor_id

program device id as 0xCD80::

    # echo CD80 >> device_id

program BAR0 size as 1MB::

    # echo 100000 >> bar0_size

check for programmed bar0 size::

    # cat bar0_size

Program BAR0 Address as DDR (0x2100000). This is the physical address of
memory, which is to be made visible to PCIe host. Similarly any other peripheral
can also be made visible to PCIe host. E.g., if you program base address of UART
as BAR0 address then when this device will be connected to a host, it will be
visible as UART.

INTA 설정과 link-up

INTA를 사용하려면 `int_type`에 `INTA`를 쓰고 `link`에 `UP`을 씁니다. Gadget link-up이 끝난 뒤에만 host를 initialize하고 해당 port의 PCIe device 검색을 시작해야 합니다.

# echo INTA >> int_type
# echo UP >> link
# cat link

`link`가 `UP`을 반환할 때까지 기다립니다. INTA를 assert하려면 `inta`에 1을, de-assert하려면 0을 씁니다.

# echo 1 >> inta
# echo 0 >> inta

::

    # echo 2100000 >> bar0_address

program interrupt type : INTA::

    # echo INTA >> int_type

go for link up now::

    # echo UP >> link

It will have to be insured that, once link up is done on gadget, then only host
is initialized and start to search PCIe devices on its port.

::

    /*wait till link is up*/
    # cat link

Wait till it returns UP.

To assert INTA::

    # echo 1 >> inta

To de-assert INTA::

    # echo 0 >> inta

MSI 설정과 전송

MSI를 사용하려면 필요한 vector 수를 먼저 `no_of_msi`에 씁니다. 예제는 4개를 요청한 뒤 `int_type`을 `MSI`로 설정하고 link를 올립니다.

# echo 4 >> no_of_msi
# echo MSI >> int_type
# echo UP >> link
# cat link

Application은 `link`가 `UP`이 될 때까지 반복해 읽되 각 read 사이에서 sleep할 수 있습니다. 그 다음 `no_of_msi`가 요청한 vector 수 4를 반환할 때까지 기다립니다. MSI vector 2를 보내려면 `send_msi`에 2를 씁니다.

# cat no_of_msi
# echo 2 >> send_msi
# cd -

if MSI is to be used as interrupt, program no of msi vector needed (say4)::

    # echo 4 >> no_of_msi

select MSI as interrupt type::

    # echo MSI >> int_type

go for link up now::

    # echo UP >> link

wait till link is up::

    # cat link

An application can repetitively read this node till link is found UP. It can
sleep between two read.

wait till msi is enabled::

    # cat no_of_msi

Should return 4 (number of requested MSI vector)

to send msi vector 2::

    # echo 2 >> send_msi
    # cd -