[SeaBIOS] [PATCH V2] pci: fixes to allow booting from extra root pci buses.
Marcel Apfelbaum
marcel at redhat.com
Thu Jun 11 16:12:33 CEST 2015
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 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 prev path includes both the extra root bridge and *then* the usual host bridge.
/pci-root at 1/pci at 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 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.
>
> -Kevin
>
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