On Thu, Jun 11, 2015 at 04:37:08PM +0300, Marcel Apfelbaum wrote:
The fixes solves the following issue: The PXB device exposes a new pci root bridge with the fw path: /pci-root@4/..., in which 4 is the root bus number. Before this patch the fw path was wrongly computed: /pci-root@1/pci@i0cf8/... Fix the above issues: Correct the bus number and remove the extra host bridge description.
Why is that wrong? The previous path looks correct to me.
The IEEE Std 1275-1994:
IEEE Standard for Boot (Initialization Configuration) Firmware: Core Requirements and Practices 3.2.1.1 Node names Each node in the device tree is identified by a node name using the following notation: driver-name@unit-address:device-arguments
The driver name field is a sequence of between one and 31 letters [...]. By convention, this name includes the name of the device’s manufacturer and the device’s model name separated by a “,”. The unit address field is the text representation of the physical address of the device within the address space defined by its parent node. The form of the text representation is bus-dependent.
Note the "physical address" part in the above. Your patch changes the "pci-root@" syntax to use a logical address instead of a physical address. That is, unless I've missed something, SeaBIOS today uses a physical address (the n'th root bus) and the patch would change it to use a logical address.
One of the goals of using an "openfirmware" like address was so that they would be stable across boots (the same mechanism is also used with coreboot). Using a physical address is key for this, because simply adding or removing a PCI device could cause the logical PCI bridge enumeration to change - and that would mess up the bootorder list if it was based on logical addresses.
-Kevin