On 06/11/2015 04:58 PM, Kevin O'Connor wrote:
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 prev path includes both the extra root bridge and *then* the usual host
bridge.
/pci-root@1/pci@i0cf8/ ...
^ new ^ regular ^ devices
Since the new pci root bridge (and bus) is on "paralel" with the regular one.
it is not correct to add it to the path.
The architecture is:
/<host bridge>/devices...
/extra root bridge/devices...
/extra root bridge/devices...
And not
/extra root bridge//<host bridge>/devices
Thanks,
Marcel
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
