Documentation: ACPI: enumeration: add PCI hierarchy representation

For "fixed" PCI devices, such as chips directly soldered
on the main board (ethernet, Wi-Fi, serial ports, etc.),
it is possible to find an ACPI enumeration.

This allows to add useful properties to these devices.
Just for an example: the property "gpio-line-names" can be
added to the pins of a GPIO expander on the PCI bus.

In order to find the ACPI name of a PCI device, it's necessary
to disassemble the BIOS ACPI tables (in particular the DSDT)
and also to analyze the PCI bus topology of the board.

This patch, with a practical example, show how to do this.

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Flavio Suligoi 2020-11-20 12:11:25 +01:00 committed by Rafael J. Wysocki
parent a8b6cfdf97
commit 390029c27e
1 changed files with 154 additions and 0 deletions

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@ -461,3 +461,157 @@ Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible"
property returned by it is meaningless. property returned by it is meaningless.
Refer to :doc:`DSD-properties-rules` for more information. Refer to :doc:`DSD-properties-rules` for more information.
PCI hierarchy representation
============================
Sometimes could be useful to enumerate a PCI device, knowing its position on the
PCI bus.
For example, some systems use PCI devices soldered directly on the mother board,
in a fixed position (ethernet, Wi-Fi, serial ports, etc.). In this conditions it
is possible to refer to these PCI devices knowing their position on the PCI bus
topology.
To identify a PCI device, a complete hierarchical description is required, from
the chipset root port to the final device, through all the intermediate
bridges/switches of the board.
For example, let us assume to have a system with a PCIe serial port, an
Exar XR17V3521, soldered on the main board. This UART chip also includes
16 GPIOs and we want to add the property ``gpio-line-names`` [1] to these pins.
In this case, the ``lspci`` output for this component is::
07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03)
The complete ``lspci`` output (manually reduced in length) is::
00:00.0 Host bridge: Intel Corp... Host Bridge (rev 0d)
...
00:13.0 PCI bridge: Intel Corp... PCI Express Port A #1 (rev fd)
00:13.1 PCI bridge: Intel Corp... PCI Express Port A #2 (rev fd)
00:13.2 PCI bridge: Intel Corp... PCI Express Port A #3 (rev fd)
00:14.0 PCI bridge: Intel Corp... PCI Express Port B #1 (rev fd)
00:14.1 PCI bridge: Intel Corp... PCI Express Port B #2 (rev fd)
...
05:00.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
06:01.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
06:02.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
06:03.0 PCI bridge: Pericom Semiconductor Device 2404 (rev 05)
07:00.0 Serial controller: Exar Corp. XR17V3521 Dual PCIe UART (rev 03) <-- Exar
...
The bus topology is::
-[0000:00]-+-00.0
...
+-13.0-[01]----00.0
+-13.1-[02]----00.0
+-13.2-[03]--
+-14.0-[04]----00.0
+-14.1-[05-09]----00.0-[06-09]--+-01.0-[07]----00.0 <-- Exar
| +-02.0-[08]----00.0
| \-03.0-[09]--
...
\-1f.1
To describe this Exar device on the PCI bus, we must start from the ACPI name
of the chipset bridge (also called "root port") with address::
Bus: 0 - Device: 14 - Function: 1
To find this information is necessary disassemble the BIOS ACPI tables, in
particular the DSDT (see also [2])::
mkdir ~/tables/
cd ~/tables/
acpidump > acpidump
acpixtract -a acpidump
iasl -e ssdt?.* -d dsdt.dat
Now, in the dsdt.dsl, we have to search the device whose address is related to
0x14 (device) and 0x01 (function). In this case we can find the following
device::
Scope (_SB.PCI0)
{
... other definitions follow ...
Device (RP02)
{
Method (_ADR, 0, NotSerialized) // _ADR: Address
{
If ((RPA2 != Zero))
{
Return (RPA2) /* \RPA2 */
}
Else
{
Return (0x00140001)
}
}
... other definitions follow ...
and the _ADR method [3] returns exactly the device/function couple that
we are looking for. With this information and analyzing the above ``lspci``
output (both the devices list and the devices tree), we can write the following
ACPI description for the Exar PCIe UART, also adding the list of its GPIO line
names::
Scope (_SB.PCI0.RP02)
{
Device (BRG1) //Bridge
{
Name (_ADR, 0x0000)
Device (BRG2) //Bridge
{
Name (_ADR, 0x00010000)
Device (EXAR)
{
Name (_ADR, 0x0000)
Name (_DSD, Package ()
{
ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
Package ()
{
Package ()
{
"gpio-line-names",
Package ()
{
"mode_232",
"mode_422",
"mode_485",
"misc_1",
"misc_2",
"misc_3",
"",
"",
"aux_1",
"aux_2",
"aux_3",
}
}
}
})
}
}
}
}
The location "_SB.PCI0.RP02" is obtained by the above investigation in the
dsdt.dsl table, whereas the device names "BRG1", "BRG2" and "EXAR" are
created analyzing the position of the Exar UART in the PCI bus topology.
References
==========
[1] Documentation/firmware-guide/acpi/gpio-properties.rst
[2] Documentation/admin-guide/acpi/initrd_table_override.rst
[3] ACPI Specifications, Version 6.3 - Paragraph 6.1.1 _ADR Address)
https://uefi.org/sites/default/files/resources/ACPI_6_3_May16.pdf,
referenced 2020-11-18