On 09/23/2015 01:01 AM, Arnd Bergmann wrote:
On Tuesday 22 September 2015 16:49:15 David Daney wrote:
From: David Daney <david.daney@xxxxxxxxxx>
There are two problems with the bus_max calculation:
1) The u8 data type can overflow for large config space windows.
2) The calculation is incorrect for a bus range that doesn't start at
zero.
Since the configuration space is relative to bus zero, make bus_max
just be the size of the config window scaled by bus_shift. Then clamp
it to a maximum of 255, per PCI. Use a data type of int to avoid
overflow problems.
Update host-generic-pci.txt to clarify the semantics of the "reg"
property with respect to non-zero starting bus numbers.
Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
Not sure about this one
diff --git a/Documentation/devicetree/bindings/pci/host-generic-pci.txt b/Documentation/devicetree/bindings/pci/host-generic-pci.txt
index cf3e205..105a968 100644
--- a/Documentation/devicetree/bindings/pci/host-generic-pci.txt
+++ b/Documentation/devicetree/bindings/pci/host-generic-pci.txt
@@ -34,7 +34,9 @@ Properties of the host controller node:
- #size-cells : Must be 2.
- reg : The Configuration Space base address and size, as accessed
- from the parent bus.
+ from the parent bus. The base address corresponds to
+ bus zero, even though the "bus-range" property may specify
+ a different starting bus number.
This sounds like very unusual behavior. If you have a system with faked
bus numbers where the registers only physically exist for a subset of the
buses, this requires defining a reg property that contains MMIO space
which is outside of the device and potentially contains other devices.
The pci-host-generic driver only maps the ranges that correspond to the
"bus-range" buses, so mapping of illegal address ranges should not be a
problem.
What would break if we instead defined it the expected way and only
list the registers for the bus numbers in the "bus-range" property?
I'm not sure if we have the luxury of being able to change the
definition, although the existing code only works with a starting bus
number of zero. From this we might conclude that non-zero starting bus
numbers cannot exist in the wild, so changing the the definition of
"reg" so that it starts at the starting bus number might be possible.
My reading of:
http://www.o3one.org/hwdocs/openfirmware/pci_supplement_2_1.pdf
Section 3.1.1, does not preclude your interpretation. Although that is
for PCI-PCI bridges, and not this pci-host-generic root complex.
If we really want to go with a different definition of what the "reg"
property means, then actual code has to change, and we risk breaking
something.
David Daney
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