[coreboot] HT chains fixup

Marc Jones marcj303 at gmail.com
Thu Nov 20 19:13:14 CET 2008

On Wed, Nov 19, 2008 at 9:16 PM, Myles Watson <mylesgw at gmail.com> wrote:
>> -----Original Message-----
>> From: Marc Jones [mailto:marcj303 at gmail.com]
>> Sent: Wednesday, November 19, 2008 4:11 PM
>> To: Myles Watson
>> Subject: Re: [coreboot] HT chains fixup
>> Myles,
>> Hi, sorry to take so long to look at this. I have some possibly dumb
>> questions.
> No problem.  I appreciate the review.
>> What is gained by knowing the ht path?
> When a HT chain is powered on, all the devices have the same UnitID (0)
> The subordinate busses get assigned bus numbers in the order that they are
> found by PCI scan, but they are found in the order of the chain.  As you
> assign each a device number, another device is visible at device 0 until the
> end of the chain is found.

But I think that the unitid scan happens before and device/dts is used
or called. This has to be done to set the HT link speed. See
northbridge\amd\k8\incoherent_ht.c. By the time the device code starts
they are setup and the bus can be scanned as normal pci.

>> Every HT bridge/tunnel under a
>> CPU acts like a PCI device. Linux doesn't know about HT and I am not
>> sure that the dts needs to.
> That's why I made ht devices morph into pci devices at chain enumeration
> time.  Once they're assigned UnitIDs it doesn't matter where they are in the
> chain.

Because it is a unitid bus number it is already numbered. I think that
the device code should use any  bus number already set. That would be
equivalent to setting the bus number with pci_x@ in the dts.

>> The exception being that coreboot needs to
>> know the CPU that the bus comes off of.  I feel like I am missing
>> something obvious that you, Ron, and others understand.
> I'm getting just as much push back from everyone else.  I'm not sure anyone
> understands the code that well.  I feel silly for having to rewrite so much
> of it.  It probably points to my lack of understanding.
>> What are you describing with and ht@? For example:
>> +                     ht at 0,a {
>> +
> /config/("southbridge/amd/amd8132/pcix.dts");
>> +                     };
>> +                     pci_a at 0,1{
>> +
> /config/("southbridge/amd/amd8132/apic.dts");
> ht at 0,a is ht chain 0, UnitID a.  I wanted it to be explicit where the chains
> end and what the numbers are.  The way the code works is that it takes the
> HT device and all the PCI devices that it implements off the list at once.
> Without knowing which devices are HT, that's hard to tell.  The code before
> used a heuristic and a lot of #if statements.

How does the code treat an ht device differently at this point?

> The reason I put pci_a here is that otherwise device 0,1 of the 8132
> collides with 0,1 of the 8111 (their dts names are the same.)
> The reason for specifying the chain number is that devices could be inserted
> in a lot of places, and it is nice to be able to specify which one you mean.
> Think of an 8-way box where you could replace any of the processors with a
> co-processor.  It gets ugly in a hurry.

So shouldn't you treat it like any bridge? ( I think this is how
bridges should be treated.)

pci at 0,1{
  /config/bridge dts
  pci at 0,0{
    /config/device dts

Since ht bridges are getting special names should pci bridges? pcib at x,y

>> Another nit I have is that pci_18_0 is the top device. Physically it
>> is but logically it isn't. The dts doesn't make sense when you compare
>> it with the lspci. I don't know if this is really better but maybe
>> something like this:
> My next patches will move everything from being a child of 18.0 to being a
> child of the domain.  That's assuming I ever get agreement for what I'm
> doing :)  I plan to have it look like this:
> domain {
>        /k8/domain
>        ht at 0,a
>        ht at 0,6
>        pci at 18,0
>        pci at 18,1
>        pci at 18,2
>        pci at 18,3
>        pci at 19,0
>        ...
> };

So a ht link off of another cpu  will be a new domain? Do you know how
the 8151 will be defined in the Serengeti dts?

>> >    domain_0_pci_18_0_ht_0_6(PCI: 00:06.0): enabled 1 have_resources 0
> This will be domain_0_ht_0_6 if I get my way.


>> What if this were a real PCI to PCI bridge? Would it be
>> domain_0_pci_18_0_pci_0_6?
> Yes, but there's no such thing with an Opteron, right?  It would have to be
> another level down in the hierarchy like domain_0_ht_0_6_pci_6_0 (remember
> that HT UnitID and PCI dev are the same, so ht_0_6 becomes pci_6_0.)

I meant if the ht bridge that acts like a pci bridge were a real pci
bridge. I think then it is domain_0_pci_18_0_pci_0_6.

>> >     domain_0_pci_18_0_ht_0_6_pci_0_0(PCI: 01:00.0): enabled 1
>> have_resources
>> > 0
>> Why isn't this domain_0_pci_18_0_ht_0_6_pci_1_0_0?
> Bus numbers get assigned as they're discovered, so they aren't mentioned in
> the dts.  That's why the 8111 has to be at 0x6 and the 8132 has to be at
> 0xa, otherwise the 8132's busses get numbered first, and  the southbridge
> ends up on bus 3.  Actually the 8111 just has to have a lower number.  0x0
> and 0x2 also work.

This is what I noted above. Devices under a bridge need to be in the
bridge brackets so you know where they are regardless of bus

>> >     domain_0_pci_18_0_ht_0_6_pci_0_1(PCI: 01:00.1): enabled 1
>> have_resources
>> > 0
>> ...
>> >    domain_0_pci_18_0_pci_6_1_0(PCI: 00:07.0): enabled 1 have_resources 0
>> I really don't understand this one. It is a device on bus 0 so what
>> does 6_1_0 mean?
> It's device 1 function 0 of the pci_6 ht device.  Remember I had to add the
> _6 so that it wouldn't have the same name as pci_a_1_0.  I agree it's
> confusing.  I couldn't think of a really great way to do it.  Maybe just
> taking out the extra underscore would help:
> domain_0_pci6_0_1
> or naming it explicitly
> domain_0_pciht6_0_1
> I'm open to suggestions.

This still doesn't make sense to me. It is on the silicon that happens
to be a HT device but it is just a pci device on bus 0. Think of it in
terms of any other motherboard device. The device is always at the
same location in the system. This one happens to be set to unitid+1. I
think that you still set it in the dts as pci at 0,7.

>> > Here are some of the next steps:
>> > - Get video working.
>> Do you know where the breakage is?
> I think it's in resource allocation.  It's really hard to follow, though.
> In the end the 8132 claims the address space that should be for the video
> buffer, and it never gets to the card.

Is the Subtractive or VGA bits set in the 8132 bridge or is the BAR
claiming the area?


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