Re: [PATCH 16/16 v6] PCI: document the new PCI boot parameters

[Yu Zhao <yu.zhao@uniscape.net>]

Greg KH wrote:
> On Fri, Nov 07, 2008 at 04:35:47PM +0800, Zhao, Yu wrote:
>> Greg KH wrote:
>>> On Fri, Nov 07, 2008 at 04:17:02PM +0800, Zhao, Yu wrote:
>>>>> Well, to do it "correctly" you are going to have to tell the driver to
>>>>> shut itself down, and reinitialize itself.
>>>>> Turns out, that doesn't really work for disk and network devices without
>>>>> dropping the connection (well, network devices should be fine probably).
>>>>> So you just can't do this, sorry.  That's why the BIOS handles all of
>>>>> these issues in a PCI hotplug system.
>>>>> How does the hardware people think we are going to handle this in the
>>>>> OS?  It's not something that any operating system can do, is it part of
>>>>> the IOV PCI spec somewhere?
>>>> No, it's not part of the PCI IOV spec.
>>>>
>>>> I just want the IOV (and whole PCI subsystem) have more flexibility on 
>>>> various BIOSes. So can we reconsider about resource rebalance as boot 
>>>> option, or should we forget about this idea?
>>> As you have proposed it, the boot option will not work at all, so I
>>> think we need to forget about it.  Especially if it is not really
>>> needed.
>> I guess at least one thing would work if people don't want to boot twice: 
>> give the bus number 0 as rebalance starting point, then all system 
>> resources would be reshuffled :-)
> 
> Hm, but don't we do that today with our basic resource reservation logic
> at boot time?  What would be different about this kind of proposal?

The generic PCI core can do this but this feature is kind of disabled by 
low level PCI code in x86. The low level code tries to reserve resource 
according to configuration from BIOS. If the BIOS is wrong, the 
allocation would fail and the generic PCI core couldn't repair it 
because the bridge resources may have been allocated by the PCI low 
level and the PCI core can't expand them to find enough resource for the 
subordinates.

The proposal is to disable x86 PCI low level to allocation resources 
according to BIOS so PCI core can fully control the resource allocation. 
The PCI core takes all resources from BARs it knows into account and 
configure the resource windows on the bridges according to its own 
calculation.

Regards,
Yu