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pci: Update documentation to make 'compatible' string optional

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Reword the documentation to make it clear the compatible string is now
optional, yet still matching on it takes precedence over PCI IDs and
PCI classes.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
This commit is contained in:
Marek Vasut 2018-10-10 21:27:07 +02:00 committed by Tom Rini
parent 02e4d38d87
commit 92ed986521
1 changed files with 9 additions and 5 deletions
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14
doc/driver-model/pci-info.txt
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@ -34,11 +34,15 @@ under that bus.
Note that this is all done on a lazy basis, as needed, so until something is
touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
PCI devices can appear in the flattened device tree. If they do this serves to
specify the driver to use for the device. In this case they will be bound at
first. Each PCI device node must have a compatible string list as well as a
<reg> property, as defined by the IEEE Std 1275-1994 PCI bus binding document
v2.1. Note we must describe PCI devices with the same bus hierarchy as the
PCI devices can appear in the flattened device tree. If they do, their node
often contains extra information which cannot be derived from the PCI IDs or
PCI class of the device. Each PCI device node must have a <reg> property, as
defined by the IEEE Std 1275-1994 PCI bus binding document v2.1. Compatible
string list is optional and generally not needed, since PCI is discoverable
bus, albeit there are justified exceptions. If the compatible string is
present, matching on it takes precedence over PCI IDs and PCI classes.
Note we must describe PCI devices with the same bus hierarchy as the
hardware, otherwise driver model cannot detect the correct parent/children
relationship during PCI bus enumeration thus PCI devices won't be bound to
their drivers accordingly. A working example like below: