Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Kinney, Michael D]

There may also be some PCI terminology differences.

The EDK II implements the PI Specifications.  Latest PI version:

  http://www.uefi.org/sites/default/files/resources/PI%201.5.zip

Volume 5 - Chapter 10 PCI Host Bridge provides the terminology that is used
for the EDK II implementation.

Specifically, Section 10.4 provides a discussion of the following example
PCI Architectures:

* Desktop system with 1 PCI root bridge
* Server system with 4 PCI root bridges
* Server system with 2 PCI segments
* Server system with 2 PCI host buses

One additional element I have noticed, is the difference between a HW
description of the platform's PCI subsystem, and the SW view of the 
platform's PCI subsystem.

Mike


-Original Message-
From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Johnson, 
Brian (EXL - Eagan)
Sent: Wednesday, May 31, 2017 8:02 AM
To: Bill Paul <wp...@windriver.com>; edk2-de...@ml01.01.org
Cc: edk2-de...@ml01.01.org; Vladimir Olovyannikov 
<vladimir.olovyanni...@broadcom.com>; Ard Biesheuvel <ard.biesheu...@linaro.org>
Subject: Re: [edk2] Using a generic PciHostBridgeDxe driver for a 
multi-PCIe-domain platform



-Original Message-
From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Bill Paul
Sent: Tuesday, May 30, 2017 12:34 PM
To: edk2-de...@ml01.01.org
Cc: edk2-de...@ml01.01.org; Vladimir Olovyannikov 
<vladimir.olovyanni...@broadcom.com>; Ard Biesheuvel <ard.biesheu...@linaro.org>
Subject: Re: [edk2] Using a generic PciHostBridgeDxe driver for a 
multi-PCIe-domain platform

Of all the gin joints in all the towns in all the world, Vladimir Olovyannikov 
had to walk into mine at 09:49:16 on Tuesday 30 May 2017 and say:

> > -Original Message-
> > From: Ard Biesheuvel [mailto:ard.biesheu...@linaro.org]
> > Sent: May-30-17 9:35 AM
> > To: Vladimir Olovyannikov
> > Cc: edk2-devel@lists.01.org
> > Subject: Re: Using a generic PciHostBridgeDxe driver for a 
> > multi-PCIe-domain platform
> > 
> > On 30 May 2017 at 16:23, Vladimir Olovyannikov
> > 
> > <vladimir.olovyanni...@broadcom.com> wrote:
> > > Hi,
> > > 
> > > I've started PCIe stack implementation design for an armv8 aarch64 
> > > platform.
> > > The platform's PCIe represents several host bridges, and each 
> > > hostbridge has one rootbridge.
> > > They do not share any resources between each other.
> > > Looking into the PciHostBridgeDxe implementation I can see that it 
> > > supports only one hostbridge, and there is a comment:
> > > // Most systems in the world including complex servers have only 
> > > one Host Bridge.
> > > 
> > > So in my case should I create my own PciHostBridgeDxe driver 
> > > supporting multiple hostbridges and do not use the Industry 
> > > standard
> > 
> > driver?
> > 
> > > I am very new to it, and will appreciate any help or idea.
> > 
> > As far as I can tell, PciHostBridgeLib allows you to return an 
> > arbitrary number of PCI host bridges, each with their own segment 
> > number. I haven't tried it myself, but it is worth a try whether 
> > returning an array of all host bridges on your platform works as 
> > expected.
> 
> Thank you Ard,
> Right, but PciHostBridgeDxe seems to work with one hostbridge.
> I am confused that
> 
> // Make sure all root bridges share the same ResourceAssigned value
> 
> The rootbridges are independent on the platform, and should not share 
> anything. Or am I missing anything?
> Anyway, I will try to return multiple hostbridges in the PciHostBridgeLib.

This may be an Intel-ism.

Note that for PCIe, I typically refer to "host bridges" as root complexes.

On PowerPC SoCs that I've worked with (e.g. Freescale/NXP MPC8548, P2020, 
P4080, T4240) there are often several root complexes. A typical board design 
may have several PCIe slots where each slot is connected to one root complex in 
the SoC. Each root complex is therefore the parent of a separate "segment" 
which has its own unique bus/dev/func space. Each root complex has its own bank 
of registers to control it, including a separate set of configuration space 
access registers. This means you can have multiple PCIe trees each with its own 
bus0/dev0/func0 root. There can therefore be several devices with the same 
bus/dev/func tuple, but which reside on separate segments.

The ARMv8 board you're working with is probably set up the same way. I've only 
worked with ARM Cortex-A boards and those have all had just one PCIe root 
complex, but it stands to reason those that have multiple root complexes would 
follow the same pattern as the PPC devices.

Intel systems can (and often do) also have multiple PCIe roo

Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Johnson, Brian (EXL - Eagan)]

-Original Message-
From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Bill Paul
Sent: Tuesday, May 30, 2017 12:34 PM
To: edk2-de...@ml01.01.org
Cc: edk2-de...@ml01.01.org; Vladimir Olovyannikov 
<vladimir.olovyanni...@broadcom.com>; Ard Biesheuvel <ard.biesheu...@linaro.org>
Subject: Re: [edk2] Using a generic PciHostBridgeDxe driver for a 
multi-PCIe-domain platform

Of all the gin joints in all the towns in all the world, Vladimir Olovyannikov 
had to walk into mine at 09:49:16 on Tuesday 30 May 2017 and say:

> > -Original Message-
> > From: Ard Biesheuvel [mailto:ard.biesheu...@linaro.org]
> > Sent: May-30-17 9:35 AM
> > To: Vladimir Olovyannikov
> > Cc: edk2-devel@lists.01.org
> > Subject: Re: Using a generic PciHostBridgeDxe driver for a 
> > multi-PCIe-domain platform
> > 
> > On 30 May 2017 at 16:23, Vladimir Olovyannikov
> > 
> > <vladimir.olovyanni...@broadcom.com> wrote:
> > > Hi,
> > > 
> > > I've started PCIe stack implementation design for an armv8 aarch64 
> > > platform.
> > > The platform's PCIe represents several host bridges, and each 
> > > hostbridge has one rootbridge.
> > > They do not share any resources between each other.
> > > Looking into the PciHostBridgeDxe implementation I can see that it 
> > > supports only one hostbridge, and there is a comment:
> > > // Most systems in the world including complex servers have only 
> > > one Host Bridge.
> > > 
> > > So in my case should I create my own PciHostBridgeDxe driver 
> > > supporting multiple hostbridges and do not use the Industry 
> > > standard
> > 
> > driver?
> > 
> > > I am very new to it, and will appreciate any help or idea.
> > 
> > As far as I can tell, PciHostBridgeLib allows you to return an 
> > arbitrary number of PCI host bridges, each with their own segment 
> > number. I haven't tried it myself, but it is worth a try whether 
> > returning an array of all host bridges on your platform works as 
> > expected.
> 
> Thank you Ard,
> Right, but PciHostBridgeDxe seems to work with one hostbridge.
> I am confused that
> 
> // Make sure all root bridges share the same ResourceAssigned value
> 
> The rootbridges are independent on the platform, and should not share 
> anything. Or am I missing anything?
> Anyway, I will try to return multiple hostbridges in the PciHostBridgeLib.

This may be an Intel-ism.

Note that for PCIe, I typically refer to "host bridges" as root complexes.

On PowerPC SoCs that I've worked with (e.g. Freescale/NXP MPC8548, P2020, 
P4080, T4240) there are often several root complexes. A typical board design 
may have several PCIe slots where each slot is connected to one root complex in 
the SoC. Each root complex is therefore the parent of a separate "segment" 
which has its own unique bus/dev/func space. Each root complex has its own bank 
of registers to control it, including a separate set of configuration space 
access registers. This means you can have multiple PCIe trees each with its own 
bus0/dev0/func0 root. There can therefore be several devices with the same 
bus/dev/func tuple, but which reside on separate segments.

The ARMv8 board you're working with is probably set up the same way. I've only 
worked with ARM Cortex-A boards and those have all had just one PCIe root 
complex, but it stands to reason those that have multiple root complexes would 
follow the same pattern as the PPC devices.

Intel systems can (and often do) also have multiple PCIe root complexes, 
however for the sake of backwards compatibility, they all end up sharing the 
same configuration space access registers (0xCF8/0xCFC or memory mapped 
extended config space) and share a single unified bus/dev/func tree.

Note that the tree is not always contiguous. For example, I've seen one Intel 
board where there was a special PCIe device on bus 128. In the ACPI tables, 
there were two PCI "segments" described, the second of which corresponded to 
bus 128. There was no switch or bridge to connect bus 128 to the tree rooted at 
bus0/dev0/func0, so it would not be possible to automatically discover it by 
just walking the bus0/dev0/func0 tree and all its branches: you needed to use 
the ACPI hint to know it was there.

I have also seen cases like this with pre-PCIe systems. For example, I've seen 
a Dell server that had both 32-bit and 64-bit PCI buses, where the 64-bit bus 
was at bus 1, but was not directly bridged to bus 0 (the 32-bit bus). There was 
a reason for this: 64-bit PCIe buses are usually clocked at 66MHz, but will 
fall back to 33MHz if you connect a 32-bit PCI device to them (this is 
supported for backward compatibility).

Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Vladimir Olovyannikov]

> -Original Message-
> From: Laszlo Ersek [mailto:ler...@redhat.com]
> Sent: May-30-17 1:17 PM
> To: Vladimir Olovyannikov; edk2-devel@lists.01.org
> Cc: Ard Biesheuvel
> Subject: Re: [edk2] Using a generic PciHostBridgeDxe driver for a
> multi-PCIe-
> domain platform
>
> On 05/30/17 21:04, Vladimir Olovyannikov wrote:
>
> > So basically my PciHostBridgeLib should treat hostbridges as
> > rootbridges with different segments in this case?
>
> In my opinion, yes.
>
> I would actually put it as
>
>   treat the set of sole root bridges on all the host bridges as multiple
>   root bridges on a single host bridge, just with different segment
>   numbers
>
> The separate segment numbers should be mapped to the separate ECAM
> windows in your PciSegmentLib instance, in my opinion.
OK, got it. Thanks a lot for your help!
>
> Thanks,
> Laszlo
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Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Laszlo Ersek]

On 05/30/17 21:04, Vladimir Olovyannikov wrote:

> So basically my PciHostBridgeLib should treat hostbridges as
> rootbridges with different segments in this case?

In my opinion, yes.

I would actually put it as

  treat the set of sole root bridges on all the host bridges as multiple
  root bridges on a single host bridge, just with different segment
  numbers

The separate segment numbers should be mapped to the separate ECAM
windows in your PciSegmentLib instance, in my opinion.

Thanks,
Laszlo
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Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Vladimir Olovyannikov]

> -Original Message-
> From: Laszlo Ersek [mailto:ler...@redhat.com]
> Sent: May-30-17 11:50 AM
> To: Vladimir Olovyannikov; edk2-devel@lists.01.org
> Cc: Ard Biesheuvel
> Subject: Re: [edk2] Using a generic PciHostBridgeDxe driver for a
> multi-PCIe-
> domain platform
>
> On 05/30/17 20:32, Laszlo Ersek wrote:
> > On 05/30/17 18:23, Vladimir Olovyannikov wrote:
> >> Hi,
> >>
> >> I've started PCIe stack implementation design for an armv8 aarch64
> >> platform.
> >> The platform's PCIe represents several host bridges, and each
> >> hostbridge has one rootbridge.
> >> They do not share any resources between each other.
> >> Looking into the PciHostBridgeDxe implementation I can see that it
> >> supports only one hostbridge, and there is a comment:
> >> // Most systems in the world including complex servers have only one
> >> Host Bridge.
> >>
> >> So in my case should I create my own PciHostBridgeDxe driver
> >> supporting multiple hostbridges and do not use the Industry standard
> driver?
> >> I am very new to it, and will appreciate any help or idea.
> >
> > I think you can use PciHostBridgeDxe on this platform:
> >
> > - Implement a PciHostBridgeLib instance (see
> > ) that returns
> > PCI_ROOT_BRIDGE objects with different Segment fields, from
> > PciHostBridgeGetRootBridges().
> >
> > - Implement a PciSegmentLib instance (see
> > ) that routes the config space
> > addresses, encoded by the PCI_SEGMENT_LIB_ADDRESS() macro,
> according
> > to your platform.
> >
> > PciHostBridgeDxe and PciBusDxe should "just work" atop. To my
> > understanding, PciBusDxe delegates all config space accesses to
> > PciHostBridgeDxe, via EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL. And
> > PciHostBridgeDxe delegates all config space accesses to the platform's
> > PciSegmentLib.
>
> A small addition. Assuming the general case, i.e. when you have a
> different
> number of root bridges on each of several host bridges, you still have to
> number all those root bridges incrementally, in a curious, flat address
> space.
> And that address space is the PcieRoot(N) device path node that is
> supposed
> to start the "DevicePath" member of each PCI_ROOT_BRIDGE object that
> you return from PciHostBridgeGetRootBridges().
>
> You can read about the PcieRoot() devpath node in the UEFI 2.6 spec.
> Basically, you have
>
> ACPI_HID_DEVICE_PATH.Header = ;
> ACPI_HID_DEVICE_PATH.HID = EFI_PNP_ID (0x0a08);
> ACPI_HID_DEVICE_PATH.UID = ;
>
> The UID values used in these devpath nodes should preferably match the
> UID values of the corresponding PCI Express Root Bridge objects
> (=PNP0A08) that you expose in your ACPI tables (DSDT and/or SSDT).
Thanks for explanation Laszlo,
In my case every hostbridge has exactly one rootbridge. I will follow your
advice and will create
SegmentPciLib and platform's PciHostBridgeLib.
So basically my PciHostBridgeLib should treat hostbridges as rootbridges
with different segments in this case?
>
> Thanks
> Laszlo

Thank you,
Vladimir
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Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Laszlo Ersek]

On 05/30/17 20:32, Laszlo Ersek wrote:
> On 05/30/17 18:23, Vladimir Olovyannikov wrote:
>> Hi,
>>
>> I've started PCIe stack implementation design for an armv8 aarch64
>> platform.
>> The platform's PCIe represents several host bridges, and each hostbridge
>> has one rootbridge.
>> They do not share any resources between each other.
>> Looking into the PciHostBridgeDxe implementation I can see that it
>> supports only one hostbridge, and there is a comment:
>> // Most systems in the world including complex servers have only one Host
>> Bridge.
>>
>> So in my case should I create my own PciHostBridgeDxe driver supporting
>> multiple hostbridges and do not use the Industry standard driver?
>> I am very new to it, and will appreciate any help or idea.
> 
> I think you can use PciHostBridgeDxe on this platform:
> 
> - Implement a PciHostBridgeLib instance (see
> ) that returns
> PCI_ROOT_BRIDGE objects with different Segment fields, from
> PciHostBridgeGetRootBridges().
> 
> - Implement a PciSegmentLib instance (see
> ) that routes the config space
> addresses, encoded by the PCI_SEGMENT_LIB_ADDRESS() macro, according to
> your platform.
> 
> PciHostBridgeDxe and PciBusDxe should "just work" atop. To my
> understanding, PciBusDxe delegates all config space accesses to
> PciHostBridgeDxe, via EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL. And
> PciHostBridgeDxe delegates all config space accesses to the platform's
> PciSegmentLib.

A small addition. Assuming the general case, i.e. when you have a
different number of root bridges on each of several host bridges, you
still have to number all those root bridges incrementally, in a curious,
flat address space. And that address space is the PcieRoot(N) device
path node that is supposed to start the "DevicePath" member of each
PCI_ROOT_BRIDGE object that you return from PciHostBridgeGetRootBridges().

You can read about the PcieRoot() devpath node in the UEFI 2.6 spec.
Basically, you have

ACPI_HID_DEVICE_PATH.Header = ;
ACPI_HID_DEVICE_PATH.HID = EFI_PNP_ID (0x0a08);
ACPI_HID_DEVICE_PATH.UID = ;

The UID values used in these devpath nodes should preferably match the
UID values of the corresponding PCI Express Root Bridge objects
(=PNP0A08) that you expose in your ACPI tables (DSDT and/or SSDT).

Thanks
Laszlo
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Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Laszlo Ersek]

On 05/30/17 18:23, Vladimir Olovyannikov wrote:
> Hi,
> 
> I've started PCIe stack implementation design for an armv8 aarch64
> platform.
> The platform's PCIe represents several host bridges, and each hostbridge
> has one rootbridge.
> They do not share any resources between each other.
> Looking into the PciHostBridgeDxe implementation I can see that it
> supports only one hostbridge, and there is a comment:
> // Most systems in the world including complex servers have only one Host
> Bridge.
> 
> So in my case should I create my own PciHostBridgeDxe driver supporting
> multiple hostbridges and do not use the Industry standard driver?
> I am very new to it, and will appreciate any help or idea.

I think you can use PciHostBridgeDxe on this platform:

- Implement a PciHostBridgeLib instance (see
) that returns
PCI_ROOT_BRIDGE objects with different Segment fields, from
PciHostBridgeGetRootBridges().

- Implement a PciSegmentLib instance (see
) that routes the config space
addresses, encoded by the PCI_SEGMENT_LIB_ADDRESS() macro, according to
your platform.

PciHostBridgeDxe and PciBusDxe should "just work" atop. To my
understanding, PciBusDxe delegates all config space accesses to
PciHostBridgeDxe, via EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL. And
PciHostBridgeDxe delegates all config space accesses to the platform's
PciSegmentLib.

Thanks,
Laszlo
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Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Vladimir Olovyannikov]

> -Original Message-
> From: Bill Paul [mailto:wp...@windriver.com]
> Sent: May-30-17 10:34 AM
> To: edk2-de...@ml01.01.org
> Cc: Vladimir Olovyannikov; Ard Biesheuvel; edk2-de...@ml01.01.org
> Subject: Re: [edk2] Using a generic PciHostBridgeDxe driver for a
multi-PCIe-
> domain platform
>
> Of all the gin joints in all the towns in all the world, Vladimir
Olovyannikov had
> to walk into mine at 09:49:16 on Tuesday 30 May 2017 and say:
>
> > > -Original Message-
> > > From: Ard Biesheuvel [mailto:ard.biesheu...@linaro.org]
> > > Sent: May-30-17 9:35 AM
> > > To: Vladimir Olovyannikov
> > > Cc: edk2-devel@lists.01.org
> > > Subject: Re: Using a generic PciHostBridgeDxe driver for a
> > > multi-PCIe-domain platform
> > >
> > > On 30 May 2017 at 16:23, Vladimir Olovyannikov
> > >
> > > <vladimir.olovyanni...@broadcom.com> wrote:
> > > > Hi,
> > > >
> > > > I've started PCIe stack implementation design for an armv8 aarch64
> > > > platform.
> > > > The platform's PCIe represents several host bridges, and each
> > > > hostbridge has one rootbridge.
> > > > They do not share any resources between each other.
> > > > Looking into the PciHostBridgeDxe implementation I can see that it
> > > > supports only one hostbridge, and there is a comment:
> > > > // Most systems in the world including complex servers have only
> > > > one Host Bridge.
> > > >
> > > > So in my case should I create my own PciHostBridgeDxe driver
> > > > supporting multiple hostbridges and do not use the Industry
> > > > standard
> > >
> > > driver?
> > >
> > > > I am very new to it, and will appreciate any help or idea.
> > >
> > > As far as I can tell, PciHostBridgeLib allows you to return an
> > > arbitrary number of PCI host bridges, each with their own segment
> > > number. I haven't tried it myself, but it is worth a try whether
> > > returning an array of all host bridges on your platform works as
> > > expected.
> >
> > Thank you Ard,
> > Right, but PciHostBridgeDxe seems to work with one hostbridge.
> > I am confused that
> >
> > // Make sure all root bridges share the same ResourceAssigned value
> >
> > The rootbridges are independent on the platform, and should not share
> > anything. Or am I missing anything?
> > Anyway, I will try to return multiple hostbridges in the
PciHostBridgeLib.
>
> This may be an Intel-ism.
>
> Note that for PCIe, I typically refer to "host bridges" as root
complexes.
>
> On PowerPC SoCs that I've worked with (e.g. Freescale/NXP MPC8548,
> P2020, P4080, T4240) there are often several root complexes. A typical
board
> design may have several PCIe slots where each slot is connected to one
root
> complex in the SoC. Each root complex is therefore the parent of a
separate
> "segment"
> which has its own unique bus/dev/func space. Each root complex has its
own
> bank of registers to control it, including a separate set of
configuration space
> access registers. This means you can have multiple PCIe trees each with
its
> own bus0/dev0/func0 root. There can therefore be several devices with
the
> same bus/dev/func tuple, but which reside on separate segments.
>
> The ARMv8 board you're working with is probably set up the same way.
I've
> only worked with ARM Cortex-A boards and those have all had just one
PCIe
> root complex, but it stands to reason those that have multiple root
> complexes would follow the same pattern as the PPC devices.
>
> Intel systems can (and often do) also have multiple PCIe root complexes,
> however for the sake of backwards compatibility, they all end up sharing
the
> same configuration space access registers (0xCF8/0xCFC or memory mapped
> extended config space) and share a single unified bus/dev/func tree.
I see. Thanks for comprehensive explanation.
In my case root complexes do not share (there is no need for backward
compatibility).
So the question is - can I use PciRootBridgeDxe from MdeModulePkg, which
operates with "rootbridges" and one rootcomplex(?),
or I need to look into the way of creating my own for the platform (say
the way Juno driver was designed initially before switching to the generic
one)?
>
> Note that the tree is not always contiguous. For example, I've seen one
Intel
> board where there was a special PCIe device on bus 128. In the ACPI
tables,
> there were two PCI "segments" described, the second of which
> corresponded to bus 128. There was no switch or br

Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Bill Paul]

Of all the gin joints in all the towns in all the world, Vladimir Olovyannikov 
had to walk into mine at 09:49:16 on Tuesday 30 May 2017 and say:

> > -Original Message-
> > From: Ard Biesheuvel [mailto:ard.biesheu...@linaro.org]
> > Sent: May-30-17 9:35 AM
> > To: Vladimir Olovyannikov
> > Cc: edk2-devel@lists.01.org
> > Subject: Re: Using a generic PciHostBridgeDxe driver for a
> > multi-PCIe-domain
> > platform
> > 
> > On 30 May 2017 at 16:23, Vladimir Olovyannikov
> > 
> >  wrote:
> > > Hi,
> > > 
> > > I've started PCIe stack implementation design for an armv8 aarch64
> > > platform.
> > > The platform's PCIe represents several host bridges, and each
> > > hostbridge has one rootbridge.
> > > They do not share any resources between each other.
> > > Looking into the PciHostBridgeDxe implementation I can see that it
> > > supports only one hostbridge, and there is a comment:
> > > // Most systems in the world including complex servers have only one
> > > Host Bridge.
> > > 
> > > So in my case should I create my own PciHostBridgeDxe driver
> > > supporting multiple hostbridges and do not use the Industry standard
> > 
> > driver?
> > 
> > > I am very new to it, and will appreciate any help or idea.
> > 
> > As far as I can tell, PciHostBridgeLib allows you to return an arbitrary
> > number
> > of PCI host bridges, each with their own segment number. I haven't tried
> > it
> > myself, but it is worth a try whether returning an array of all host
> > bridges on
> > your platform works as expected.
> 
> Thank you Ard,
> Right, but PciHostBridgeDxe seems to work with one hostbridge.
> I am confused that
> 
> // Make sure all root bridges share the same ResourceAssigned value
> 
> The rootbridges are independent on the platform, and should not share
> anything. Or am I missing anything?
> Anyway, I will try to return multiple hostbridges in the PciHostBridgeLib.

This may be an Intel-ism.

Note that for PCIe, I typically refer to "host bridges" as root complexes.

On PowerPC SoCs that I've worked with (e.g. Freescale/NXP MPC8548, P2020, 
P4080, T4240) there are often several root complexes. A typical board design 
may have several PCIe slots where each slot is connected to one root complex 
in the SoC. Each root complex is therefore the parent of a separate "segment" 
which has its own unique bus/dev/func space. Each root complex has its own 
bank of registers to control it, including a separate set of configuration 
space access registers. This means you can have multiple PCIe trees each with 
its own bus0/dev0/func0 root. There can therefore be several devices with the 
same bus/dev/func tuple, but which reside on separate segments.

The ARMv8 board you're working with is probably set up the same way. I've only 
worked with ARM Cortex-A boards and those have all had just one PCIe root 
complex, but it stands to reason those that have multiple root complexes would 
follow the same pattern as the PPC devices.

Intel systems can (and often do) also have multiple PCIe root complexes, 
however for the sake of backwards compatibility, they all end up sharing the 
same configuration space access registers (0xCF8/0xCFC or memory mapped 
extended config space) and share a single unified bus/dev/func tree.

Note that the tree is not always contiguous. For example, I've seen one Intel 
board where there was a special PCIe device on bus 128. In the ACPI tables, 
there were two PCI "segments" described, the second of which corresponded to 
bus 128. There was no switch or bridge to connect bus 128 to the tree rooted 
at bus0/dev0/func0, so it would not be possible to automatically discover it 
by just walking the bus0/dev0/func0 tree and all its branches: you needed to 
use the ACPI hint to know it was there.

I have also seen cases like this with pre-PCIe systems. For example, I've seen 
a Dell server that had both 32-bit and 64-bit PCI buses, where the 64-bit bus 
was at bus 1, but was not directly bridged to bus 0 (the 32-bit bus). There 
was a reason for this: 64-bit PCIe buses are usually clocked at 66MHz, but 
will fall back to 33MHz if you connect a 32-bit PCI device to them (this is 
supported for backward compatibility). Reducing the bus clock reduces 
performance, so to avoid that it's necessary to keep the 32-bit and 64-bit 
buses separate and thus give each one its own host bridge. As with the 
previous example, all the devices shared the same bus/dev/func space, but the 
only way to learn about the other segment was to probe the ACPI tables.

It sounds as if the UEFI PCI host bridge code may be biased towards the Intel 
PCI behavior, though I'm not sure to what extent.

So the comment that you found that says:

// Most systems in the world including complex servers have only one Host
Bridge.

Should probably be amended: it should probably say "Most Intel systems" and 
even those systems probably do have more than one host bridge (root complex), 
it's just that 

Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Vladimir Olovyannikov]

> -Original Message-
> From: Ard Biesheuvel [mailto:ard.biesheu...@linaro.org]
> Sent: May-30-17 9:35 AM
> To: Vladimir Olovyannikov
> Cc: edk2-devel@lists.01.org
> Subject: Re: Using a generic PciHostBridgeDxe driver for a
> multi-PCIe-domain
> platform
>
> On 30 May 2017 at 16:23, Vladimir Olovyannikov
>  wrote:
> > Hi,
> >
> > I've started PCIe stack implementation design for an armv8 aarch64
> > platform.
> > The platform's PCIe represents several host bridges, and each
> > hostbridge has one rootbridge.
> > They do not share any resources between each other.
> > Looking into the PciHostBridgeDxe implementation I can see that it
> > supports only one hostbridge, and there is a comment:
> > // Most systems in the world including complex servers have only one
> > Host Bridge.
> >
> > So in my case should I create my own PciHostBridgeDxe driver
> > supporting multiple hostbridges and do not use the Industry standard
> driver?
> > I am very new to it, and will appreciate any help or idea.
> >
>
> As far as I can tell, PciHostBridgeLib allows you to return an arbitrary
> number
> of PCI host bridges, each with their own segment number. I haven't tried
> it
> myself, but it is worth a try whether returning an array of all host
> bridges on
> your platform works as expected.

Thank you Ard,
Right, but PciHostBridgeDxe seems to work with one hostbridge.
I am confused that

// Make sure all root bridges share the same ResourceAssigned value

The rootbridges are independent on the platform, and should not share
anything. Or am I missing anything?
Anyway, I will try to return multiple hostbridges in the PciHostBridgeLib.

Thank you,
Vladimir
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Re: [edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Ard Biesheuvel]

On 30 May 2017 at 16:23, Vladimir Olovyannikov
 wrote:
> Hi,
>
> I've started PCIe stack implementation design for an armv8 aarch64
> platform.
> The platform's PCIe represents several host bridges, and each hostbridge
> has one rootbridge.
> They do not share any resources between each other.
> Looking into the PciHostBridgeDxe implementation I can see that it
> supports only one hostbridge, and there is a comment:
> // Most systems in the world including complex servers have only one Host
> Bridge.
>
> So in my case should I create my own PciHostBridgeDxe driver supporting
> multiple hostbridges and do not use the Industry standard driver?
> I am very new to it, and will appreciate any help or idea.
>

As far as I can tell, PciHostBridgeLib allows you to return an
arbitrary number of PCI host bridges, each with their own segment
number. I haven't tried it myself, but it is worth a try whether
returning an array of all host bridges on your platform works as
expected.
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[edk2] Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Vladimir Olovyannikov]

Hi,

I've started PCIe stack implementation design for an armv8 aarch64
platform.
The platform's PCIe represents several host bridges, and each hostbridge
has one rootbridge.
They do not share any resources between each other.
Looking into the PciHostBridgeDxe implementation I can see that it
supports only one hostbridge, and there is a comment:
// Most systems in the world including complex servers have only one Host
Bridge.

So in my case should I create my own PciHostBridgeDxe driver supporting
multiple hostbridges and do not use the Industry standard driver?
I am very new to it, and will appreciate any help or idea.

Thank you,
Vladimir
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