On 2021/7/15 0:54, Bjorn Helgaas wrote:
[+cc Matthew for "lspci -P"]
On Wed, Jul 14, 2021 at 02:33:37PM +0800, Wenchao Hao wrote:
Since linux identify PCI peripheral by [domain:bus:device:function] number
like following,
# lspci -D
0000:00:00.0 Host bridge: Red Hat, Inc. QEMU PCIe Host bridge
0000:00:01.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 92)
0000:00:02.0 PCI bridge: Intel Corporation 7500/5520/5500/X58 I/O Hub PCI
Express Root Port 0 (rev 02)
0000:00:02.1 PCI bridge: Intel Corporation 7500/5520/5500/X58 I/O Hub PCI
Express Root Port 0 (rev 02)
0000:00:02.2 PCI bridge: Intel Corporation 7500/5520/5500/X58 I/O Hub PCI
Express Root Port 0 (rev 02)
0000:00:02.3 PCI bridge: Intel Corporation 7500/5520/5500/X58 I/O Hub PCI
Express Root Port 0 (rev 02)
0000:01:00.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge
0000:02:01.0 USB controller: Intel Corporation 82801DB/DBM (ICH4/ICH4-M)
USB2 EHCI Controller (rev 10)
0000:02:02.0 Unclassified device [00ff]: Virtio: Virtio memory balloon
0000:02:03.0 SCSI storage controller: Virtio: Virtio SCSI
0000:02:04.0 Display controller: Virtio: Virtio GPU (rev 01)
0000:03:00.0 Ethernet controller: Virtio: Virtio network device (rev 01)
Here are my questions: Are these [domain:bus:device:function] number
come from hardware's physical connection or allocated by software
dynamic?
The device and function numbers are completely determined by the
hardware and are not programmable.
Bus numbers are programmable and are determined by the Secondary Bus
Number of the bridge leading to the device. These bus numbers are
generally programmed by the BIOS on x86. It's possible for Linux to
reprogram them, but it generally leaves them alone if they are valid.
On x86 with ACPI, the domain number comes from the _SEG method of the
PNP0A03 device that describes the host bridge. This may correspond to
a programmable hardware register, but that isn't visible to the OS and
Linux has no way to change it.
If hardware do not change, can we guarantee these number do not
change after system reboot?
For the typical x86 system with ACPI, this is really a question for
the BIOS. If the hardware doesn't change, I would *expect* the
domain/bus/device/function numbers to stay the same, but only BIOS
folks can answer this definitively.
If they are not fixed, then is there anyway I can get a fixed ID
which can indicate physical connection.
You can look at the "lspci -P" option. I'm not really familiar with
this, but I think Matthew (cc'd) implemented it.
Bjorn
.
Thanks Bjorn for your great analysis and I would ask BIOS for their
suggestions.
I think we can put some constraints such as make BIOS give a stable bus
number on our users to meet their needs of finding a stable path,
although this method looks ugly.
Wenchao
