[SeaBIOS] [PATCH V2] pci: fixes to allow booting from extra root pci buses.
kevin at koconnor.net
Thu Jun 11 15:58:41 CEST 2015
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 at 4/..., in which 4 is the root bus number.
> Before this patch the fw path was wrongly computed:
> /pci-root at 1/pci at 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
> 126.96.36.199 Node names
> Each node in the device tree is identified by a node name
> using the following notation:
> driver-name at 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.
More information about the SeaBIOS