Re: [PATCH 11/11] vfio/igd: Update IGD passthrough documentation

["Corvin Köhne" <C.Koehne@beckhoff.com>]

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On Tue, 2025-04-22 at 00:31 +0800, Tomita Moeko wrote:
> CAUTION: External Email!!
> In previous commits, several changes were made to IGD passthrough:
> * Legacy mode now requires the IGD to be Gen6–Gen9.
> * OpRegion quirk is enabled by default.
> * "etc/igd-bdsm-size" is set to 0 when guest firmware does not need to
>   allocate Data Stolen Memory and write BDSM register.
> Update the documentation to reflect these changes.
> 
> Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
> ---
>  docs/igd-assign.txt | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/docs/igd-assign.txt b/docs/igd-assign.txt
> index 3aed7956d5..eac31ea3dd 100644
> --- a/docs/igd-assign.txt
> +++ b/docs/igd-assign.txt
> @@ -47,6 +47,7 @@ Intel document [1] shows how to dump VBIOS to file. For UEFI
> Option ROM, see
>  
>  QEMU also provides a "Legacy" mode that implicitly enables full functionality
>  on IGD, it is automatically enabled when
> +* IGD generation is 6 to 9 (Sandy Bridge to Comet Lake) 
>  * Machine type is i440fx
>  * IGD is assigned to guest BDF 00:02.0
>  * ROM BAR or romfile is present
> @@ -101,7 +102,7 @@ digital formats work well.
>  
>  Options
>  =======
> -* x-igd-opregion=[on|*off*]
> +* x-igd-opregion=[*on*|off]
>    Copy host IGD OpRegion and expose it to guest with fw_cfg
>  
>  * x-igd-lpc=[on|*off*]
> @@ -123,7 +124,7 @@ Examples
>  
>  * Adding IGD with OpRegion and LPC ID hack, but without VGA ranges
>    (For UEFI guests)
> -  -device vfio-pci,host=00:02.0,id=hostdev0,addr=2.0,x-igd-legacy-mode=off,x-
> igd-opregion=on,x-igd-lpc=on,romfile=efi_oprom.rom
> +  -device vfio-pci,host=00:02.0,id=hostdev0,addr=2.0,x-igd-legacy-mode=off,x-
> igd-lpc=on,romfile=efi_oprom.rom
>  
>  
>  Guest firmware
> @@ -156,6 +157,12 @@ fw_cfg requirements on the VM firmware:
>     it's expected that this fw_cfg file is only relevant to a single PCI
>     class VGA device with Intel vendor ID, appearing at PCI bus address
> 00:02.0.
>  
> +   Starting from Meteor Lake, IGD devices access stolen memory via its MMIO
> +   BAR2 (LMEMBAR) and removed the BDSM register in config space. There is
> +   no need for guest firmware to allocate data stolen memory in guest address
> +   space and write it to BDSM register. Value of this fw_cfg file is 0 in
> +   such case.
> +
>  Upstream Seabios has OpRegion and BDSM (pre-Gen11 device only) support.
>  However, the support is not accepted by upstream EDK2/OVMF. A recommended
>  solution is to create a virtual OpRom with following DXE drivers:

Not sure how upstream prefers handling documentation. Those are only small
changes, so I'd add them to the corresponding commits.


-- 
Kind regards,
Corvin

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