accessing PCI configuration space

Maxim

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Jun 17, 2008, 11:22:07 AM6/17/08

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Is there a way to access PCI(E) config space from user mode in Windows 2003+?
I.e., an equivalent of lspci command? Alternatively, does that information
get cached
somewhere (e.g. in the registry) by the OS?

I know a driver can read that information out, but the idea is to get access
to the
information without having to load a driver for a device.

The basic problem I am trying to solve is to determine the width of PCIE link
in the slot that my device is plugged into. The only information I can find
in the registry
is vendor/product PCI IDs and a few other things, but nothing close to a
full dump of
PCI config space.

Maxim

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Jun 17, 2008, 11:29:10 AM6/17/08

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Btw, I'll also take an answer in a form of an existing freeware application
that does not install a driver :)

Doron Holan [MSFT]

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Jun 17, 2008, 6:27:02 PM6/17/08

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starting in vista (and subsequent OS's) the current link speed is exposed
through a DEVPKEY (DEVPKEY_PciDevice_CurrentLinkSpeed in pciprop.h). before
that, you need to figure this out for yourself...

d

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Calvin Guan

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Jun 17, 2008, 7:33:57 PM6/17/08

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!pcitree
You don't need a driver, it's free. does that count?

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Maxim

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Jun 18, 2008, 12:09:00 AM6/18/08

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bummer. oh well, thanks anyhow

Maxim

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Jun 18, 2008, 9:52:00 AM6/18/08

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i don't think it does, because it does not provide a dump of PCIE config
space - only prints a few fields that are visible by other means (registry,
device property details, devcon find pci\*, etc). same goes for !devext xxx
PCI

DaveH

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Jun 18, 2008, 1:10:01 PM6/18/08

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Maxim, I'm not sure what Doron has suggested is what you're after as the link
speed (as defined by PCI Express spec) currently can only ever be 2.5Gb/s no
matter what the width of the link is.

If you really want to figure out the link width from user mode, you have to
query the Link Status Register (offset 12h of PCI Express Capability
Structure in PCI Config Space) which tells you the negotiated width of the
link (1x, 2x, etc.). To access PCI Config Space you have to use PCI host
bridge I/O ports namely CF8h and CFCh in a way described in PCI spec. In
kernel mode, you can use the deprecated HalGetBusDataByOffset (recommended
method is to create and send an IRP to PCI driver). In user mode, you could
use _inpd, _outpd on above ports in a similar way to HalGetBusDataByOffset
(check
http://www.reactos.org/generated/doxygen/d7/d7c/hal_2halx86_2generic_2pci_8c.html#a4 to know how).

That said, I don't think this would be a good approach as accesses to above
registers are not atomic and you might end up with some nasty side effects.

DaveH.

luchnikov

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Jun 20, 2008, 12:57:27 PM6/20/08

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This is Maxim, under a diff name... Do __inpb/__outpb really work in
user mode? I'd imagine that Windows does not allow user-level access
to hardware resources...

On Jun 18, 1:10 pm, DaveH <Da...@discussions.microsoft.com> wrote:
> Maxim, I'm not sure what Doron has suggested is what you're after as the link
> speed (as defined by PCI Express spec) currently can only ever be 2.5Gb/s no
> matter what the width of the link is.
>
> If you really want to figure out the link width from user mode, you have to
> query the Link Status Register (offset 12h of PCI Express Capability
> Structure in PCI Config Space) which tells you the negotiated width of the
> link (1x, 2x, etc.). To access PCI Config Space you have to use PCI host
> bridge I/O ports namely CF8h and CFCh in a way described in PCI spec. In
> kernel mode, you can use the deprecated HalGetBusDataByOffset (recommended
> method is to create and send an IRP to PCI driver). In user mode, you could
> use _inpd, _outpd on above ports in a similar way to HalGetBusDataByOffset

> (checkhttp://www.reactos.org/generated/doxygen/d7/d7c/hal_2halx86_2generic_...to know how).

Don Burn

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Jun 20, 2008, 1:08:05 PM6/20/08

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Using __inpb/__outpb is not allowed from user space in Windows. And to go
further a great way to create subtle bugs is to access the PCI Config Space
registers I know a firm being sued for doing this.

--
Don Burn (MVP, Windows DDK)
Windows 2k/XP/2k3 Filesystem and Driver Consulting
Website: http://www.windrvr.com
Blog: http://msmvps.com/blogs/WinDrvr
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luchnikov

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Jun 20, 2008, 1:29:51 PM6/20/08

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By merely reading the space? I imagine they are writing it...

Anyway, looks like w/o a filter driver I am SOL. See my other post -
I tried getting PCI config data in STORPORT miniport driver via
StorPortGetBusData, without much luck.

Too bad there isn't some IOCTL you can send to the PCI bus driver to
get this data in Win2K3

Don Burn

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Jun 20, 2008, 1:51:56 PM6/20/08

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To read a specific location in PCI config space you have to write the
address to one register, then read from the other register. Since you have
no access to the lock doing this, you can get subtle bugs of the form:

System writes address reg
User writes address reg
Systems reads "data"
User reads "data"

Of course the system is not reading what it expects!

--
Don Burn (MVP, Windows DDK)
Windows 2k/XP/2k3 Filesystem and Driver Consulting
Website: http://www.windrvr.com
Blog: http://msmvps.com/blogs/WinDrvr
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