[SeaBIOS] Re: Large 32 bit BAR's

[Wannes Bouwen (Nokia)]

Hello Daniel,

No, unfortunately this cannot be changed. So there is no possibility to map the 32 bit BAR in a higher memory region (where the 64 bit BAR’s are located)?

Kind regards,

Wannes

From: Daniel Paziyski 
Sent: Wednesday, April 12, 2023 9:19 AM
To: Wannes Bouwen (Nokia) ; [e-mail]
Subject: Re: [SeaBIOS] Large 32 bit BAR's

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Hello,

For a device with such a big 32 bit BAR, it would be a challenge to fit it inside the 32 bit window, since the RAM region available on <4GB must be specially tuned with help from the emulator (which, as far as I am aware, isn't available) to give space for BAR allocations there. Is there a possibility for that emulated PCIe device to be configured to expose a 64 bit BAR instead?

Regards,

Daniel

On 4/12/23 08:23, Wannes Bouwen (Nokia) wrote:
Hello,

I’m running a x86 QEMU with Ubuntu. On this system we want to emulate a PCIe device which contains a large 32-bit BAR (2 GiB). This is not working and I get following error:

SeaBIOS (version rel-1.14.0-0-g155821a-20210629_105355-sharpie)
BUILD: gcc: (GCC) 4.8.5 20150623 (Red Hat 4.8.5-36) binutils: version 2.27-34.base.el7
No Xen hypervisor found.
Running on QEMU (q35)
Running on KVM
Found QEMU fw_cfg
QEMU fw_cfg DMA interface supported
qemu/e820: addr 0x0000000000000000 len 0x0000000080000000 [RAM]
qemu/e820: addr 0x0000000100000000 len 0x0000000180000000 [RAM]
Relocating init from 0x000d4de0 to 0x7ffa9420 (size 93008)
Moving pm_base to 0x600
kvmclock: at 0xeb040 (msr 0x4b564d01)
kvmclock: stable tsc, 2992 MHz
CPU Mhz=2992 (kvmclock)
=== PCI bus & bridge init ===
PCI: pci_bios_init_bus_rec bus = 0x0
PCI: pci_bios_init_bus_rec bdf = 0x20
PCI: primary bus = 0x0
PCI: secondary bus = 0xff -> 0x1
PCI: pci_bios_init_bus_rec bus = 0x1
PCI: subordinate bus = 0x0 -> 0x1
=== PCI device probing ===
Found 12 PCI devices (max PCI bus is 01)
PCIe: using q35 mmconfig at 0xb0000000
=== PCI new allocation pass #1 ===
PCI: check devices
PCI: secondary bus 1 size 00000000 type io
PCI: secondary bus 1 size 100000000 type mem
PCI: secondary bus 1 size 100000000 type prefmem
=== PCI new allocation pass #2 ===
PCI: IO: c000 - c0ff
PCI: 32: 00000000c0000000 - 00000000fec00000
PCI: out of 32bit address space

I’ve had a look at the code and it seems that 32-bit BAR’s have a limited memory region available (less than 1 GiB). Is there a possibility to use such large 32-bit BAR’s in combination with SeaBios by e.g. mapping them in the higher memory region where 64-bit BAR’s are mapped?

Thanks in advance!

Kind regards,

Wannes

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