2021-02-01 19:58:09 +00:00
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.. SPDX-License-Identifier: GPL-2.0
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===================================================================
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PCI Non-Transparent Bridge (NTB) Endpoint Function (EPF) User Guide
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===================================================================
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:Author: Kishon Vijay Abraham I <kishon@ti.com>
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This document is a guide to help users use pci-epf-ntb function driver
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and ntb_hw_epf host driver for NTB functionality. The list of steps to
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be followed in the host side and EP side is given below. For the hardware
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configuration and internals of NTB using configurable endpoints see
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Documentation/PCI/endpoint/pci-ntb-function.rst
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Endpoint Device
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===============
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Endpoint Controller Devices
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---------------------------
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For implementing NTB functionality at least two endpoint controller devices
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are required.
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To find the list of endpoint controller devices in the system::
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# ls /sys/class/pci_epc/
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2900000.pcie-ep 2910000.pcie-ep
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If PCI_ENDPOINT_CONFIGFS is enabled::
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# ls /sys/kernel/config/pci_ep/controllers
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2900000.pcie-ep 2910000.pcie-ep
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Endpoint Function Drivers
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-------------------------
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To find the list of endpoint function drivers in the system::
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# ls /sys/bus/pci-epf/drivers
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pci_epf_ntb pci_epf_ntb
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If PCI_ENDPOINT_CONFIGFS is enabled::
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# ls /sys/kernel/config/pci_ep/functions
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pci_epf_ntb pci_epf_ntb
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Creating pci-epf-ntb Device
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----------------------------
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PCI endpoint function device can be created using the configfs. To create
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pci-epf-ntb device, the following commands can be used::
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# mount -t configfs none /sys/kernel/config
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# cd /sys/kernel/config/pci_ep/
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# mkdir functions/pci_epf_ntb/func1
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The "mkdir func1" above creates the pci-epf-ntb function device that will
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be probed by pci_epf_ntb driver.
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The PCI endpoint framework populates the directory with the following
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configurable fields::
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# ls functions/pci_epf_ntb/func1
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baseclass_code deviceid msi_interrupts pci-epf-ntb.0
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progif_code secondary subsys_id vendorid
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cache_line_size interrupt_pin msix_interrupts primary
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revid subclass_code subsys_vendor_id
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The PCI endpoint function driver populates these entries with default values
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when the device is bound to the driver. The pci-epf-ntb driver populates
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vendorid with 0xffff and interrupt_pin with 0x0001::
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# cat functions/pci_epf_ntb/func1/vendorid
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0xffff
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# cat functions/pci_epf_ntb/func1/interrupt_pin
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0x0001
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Configuring pci-epf-ntb Device
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-------------------------------
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The user can configure the pci-epf-ntb device using its configfs entry. In order
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to change the vendorid and the deviceid, the following
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commands can be used::
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# echo 0x104c > functions/pci_epf_ntb/func1/vendorid
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# echo 0xb00d > functions/pci_epf_ntb/func1/deviceid
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PCI: endpoint: Automatically create a function specific attributes group
A PCI endpoint function driver can define function specific attributes
under its function configfs directory using the add_cfs() endpoint driver
operation. This is done by tying up the mkdir operation for the function
configfs directory to a call to the add_cfs() operation. However, there
are no checks preventing the user from repeatedly creating function
specific attribute directories with different names, resulting in the same
endpoint specific attributes group being added multiple times, which also
result in an invalid reference counting for the attribute groups. E.g.,
using the pci-epf-ntb function driver as an example, the user creates the
function as follows:
$ modprobe pci-epf-ntb
$ cd /sys/kernel/config/pci_ep/functions/pci_epf_ntb
$ mkdir func0
$ tree func0
func0/
|-- baseclass_code
|-- cache_line_size
|-- ...
`-- vendorid
$ mkdir func0/attrs
$ tree func0
func0/
|-- attrs
| |-- db_count
| |-- mw1
| |-- mw2
| |-- mw3
| |-- mw4
| |-- num_mws
| `-- spad_count
|-- baseclass_code
|-- cache_line_size
|-- ...
`-- vendorid
At this point, the function can be started by linking the EP controller.
However, if the user mistakenly creates again a directory:
$ mkdir func0/attrs2
$ tree func0
func0/
|-- attrs
| |-- db_count
| |-- mw1
| |-- mw2
| |-- mw3
| |-- mw4
| |-- num_mws
| `-- spad_count
|-- attrs2
| |-- db_count
| |-- mw1
| |-- mw2
| |-- mw3
| |-- mw4
| |-- num_mws
| `-- spad_count
|-- baseclass_code
|-- cache_line_size
|-- ...
`-- vendorid
The endpoint function specific attributes are duplicated and cause a crash
when the endpoint function device is torn down:
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 2 PID: 834 at lib/refcount.c:25 refcount_warn_saturate+0xc8/0x144
CPU: 2 PID: 834 Comm: rmdir Not tainted 6.3.0-rc1 #1
Hardware name: Pine64 RockPro64 v2.1 (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
...
Call trace:
refcount_warn_saturate+0xc8/0x144
config_item_get+0x7c/0x80
configfs_rmdir+0x17c/0x30c
vfs_rmdir+0x8c/0x204
do_rmdir+0x158/0x184
__arm64_sys_unlinkat+0x64/0x80
invoke_syscall+0x48/0x114
...
Fix this by modifying pci_epf_cfs_work() to execute the new function
pci_ep_cfs_add_type_group() which itself calls pci_epf_type_add_cfs() to
obtain the function specific attribute group and the group name (directory
name) from the endpoint function driver. If the function driver defines an
attribute group, pci_ep_cfs_add_type_group() then proceeds to register this
group using configfs_register_group(), thus automatically exposing the
function type specific configfs attributes to the user. E.g.:
$ modprobe pci-epf-ntb
$ cd /sys/kernel/config/pci_ep/functions/pci_epf_ntb
$ mkdir func0
$ tree func0
func0/
|-- baseclass_code
|-- cache_line_size
|-- ...
|-- pci_epf_ntb.0
| |-- db_count
| |-- mw1
| |-- mw2
| |-- mw3
| |-- mw4
| |-- num_mws
| `-- spad_count
|-- primary
|-- ...
`-- vendorid
With this change, there is no need for the user to create or delete
directories in the endpoint function attributes directory. The
pci_epf_type_group_ops group operations are thus removed.
Also update the documentation for the pci-epf-ntb and pci-epf-vntb function
drivers to reflect this change, removing the explanations showing the need
to manually create the sub-directory for the function specific attributes.
Link: https://lore.kernel.org/r/20230415023542.77601-2-dlemoal@kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
2023-04-15 02:35:26 +00:00
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The PCI endpoint framework also automatically creates a sub-directory in the
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function attribute directory. This sub-directory has the same name as the name
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of the function device and is populated with the following NTB specific
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attributes that can be configured by the user::
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2021-02-01 19:58:09 +00:00
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# ls functions/pci_epf_ntb/func1/pci_epf_ntb.0/
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db_count mw1 mw2 mw3 mw4 num_mws
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spad_count
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A sample configuration for NTB function is given below::
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# echo 4 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/db_count
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# echo 128 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/spad_count
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# echo 2 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/num_mws
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# echo 0x100000 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/mw1
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# echo 0x100000 > functions/pci_epf_ntb/func1/pci_epf_ntb.0/mw2
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Binding pci-epf-ntb Device to EP Controller
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--------------------------------------------
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NTB function device should be attached to two PCI endpoint controllers
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connected to the two hosts. Use the 'primary' and 'secondary' entries
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inside NTB function device to attach one PCI endpoint controller to
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primary interface and the other PCI endpoint controller to the secondary
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interface::
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# ln -s controllers/2900000.pcie-ep/ functions/pci-epf-ntb/func1/primary
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# ln -s controllers/2910000.pcie-ep/ functions/pci-epf-ntb/func1/secondary
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Once the above step is completed, both the PCI endpoint controllers are ready to
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establish a link with the host.
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Start the Link
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--------------
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In order for the endpoint device to establish a link with the host, the _start_
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field should be populated with '1'. For NTB, both the PCI endpoint controllers
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should establish link with the host::
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# echo 1 > controllers/2900000.pcie-ep/start
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# echo 1 > controllers/2910000.pcie-ep/start
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RootComplex Device
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==================
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lspci Output
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------------
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Note that the devices listed here correspond to the values populated in
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"Creating pci-epf-ntb Device" section above::
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# lspci
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0000:00:00.0 PCI bridge: Texas Instruments Device b00d
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0000:01:00.0 RAM memory: Texas Instruments Device b00d
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Using ntb_hw_epf Device
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-----------------------
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The host side software follows the standard NTB software architecture in Linux.
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All the existing client side NTB utilities like NTB Transport Client and NTB
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Netdev, NTB Ping Pong Test Client and NTB Tool Test Client can be used with NTB
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function device.
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For more information on NTB see
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:doc:`Non-Transparent Bridge <../../driver-api/ntb>`
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