Re: [RFC 4/7] gpu: nova-core: populate GSP_VF_INFO when vGPU is enabled

[Joel Fernandes <joelagnelf@nvidia.com>]

> On Dec 12, 2025, at 9:17 AM, John Hubbard <jhubbard@nvidia.com> wrote:
> 
> On 12/11/25 5:36 PM, Joel Fernandes wrote:
>> Hi Zhi,
>>> On Tue, Dec 09, 2025 at 03:41:14PM +0200, Zhi Wang wrote:
>>> On Sat, 6 Dec 2025 21:32:51 -0500
>>> Joel Fernandes <joelagnelf@nvidia.com> wrote:
>> [..]
>>>>> 0x00000004); +
>>>>> +            let val = bar.read32(0x88000 + 0xbfc);
>>>>> +            info.b64bitBar2 = u8::from((val & 0x00000006) ==
>>>>> 0x00000004);
>>>> 
>>>> Please no magic numbers, please use proper named constants with
>>>> documentation comments explaining the values.
>>>> 
>>>> Also BAR reads here need proper register macro definitions/access.
>>>> 
>>> 
>>> That is true. :) But this is because there is no register definition in
>>> the OpenRM code/non OpenRM code as well. I have no idea about the name
>>> and bit definitions of this register.
>>> 
>>> Suppose I will have to find some clues from some folks then document
>>> them here when going to patches request for merged. :)
>> I think these magic numbers are PCIe config space related. I found a couple of references [1] [2] [3]
>> [1]
>> In Open GPU docs, I see 0x00088000 is NV_PCFG but this is on Turing, lets
>> confirm what it is on other architectures (if not common, should it go
>> through a HAL?).
> 
> It changed on Hopper. My Hopper/Blackwell series handles this.

Great, thanks for confirming, John. Zhi, you should probably rebase on the series from John then.

thanks,

 - Joel



> 
> thanks,
> John Hubbard
> 
>> https://github.com/NVIDIA/open-gpu-kernel-modules/blob/a5bfb10e75a4046c5d991c65f49b5d29151e68cf/src/common/inc/swref/published/turing/tu102/dev_nv_xve.h#L4
>> and 0xbf4 is SRIOV capability headers, per the same header file:
>> NV_XVE_SRIOV_CAP_HDR10
>> Also the bit definition is not documented in that public header, but I find
>> from internal sources that what you're trying to do with the "& 0x6" is
>> determine whether the VF BAR is capable of 64-bit addressing:
>>  Bits [2:1] is VF_BAR1_ADR_TYPE and = 2 means the BAR is capable of 64-bit
>>  addressing, and = 0 means 32-bit.
>> I wonder if the format of these capability headers are present in the PCI
>> specification? It is worth checking, I find some very similar mentions of the
>> value 2 being 64-bit in https://wiki.osdev.org/PCI as well.
>> [2]
>> In Nouveau I found the 0x88000
>>   drivers/gpu/drm/nouveau/nouveau_reg.h +684
>> With a bunch of ids and such which is typical of what is in config space:
>> #    define NV50_PBUS_PCI_ID                                0x00088000
>> #        define NV50_PBUS_PCI_ID_VENDOR_ID                  0x0000ffff
>> #        define NV50_PBUS_PCI_ID_VENDOR_ID__SHIFT                    0
>> #        define NV50_PBUS_PCI_ID_DEVICE_ID                  0xffff0000
>> #        define NV50_PBUS_PCI_ID_DEVICE_ID__SHIFT                   16
>> Perhaps this is something pdev.config_read_dword() should be giving?
>> [3] This one I am not sure off, but the link
>> https://envytools.readthedocs.io/en/latest/hw/bus/pci.html says that on NV40+
>> cards, all 0x1000 bytes of PCIE config space are mapped to MMIO register
>> space at addresses 0x88000-0x88fff. This matches exactly the magic number in
>> your patch.
>> Also, I wonder if we need to determine if the BARs can be 64-bit addressed, do
>> we have requirements for BAR sizes > 4GB for vGPU and if not, do we need to
>> determine the BAR size addressability?
>> Also, shouldn't the PCI core subsystem be automatically determining if the
>> BARs are 64-bit addressable? Not sure if that belongs in the driver. It would
>> be good to understand how this is supposed to work.
>> thanks,
>>  - Joel
>