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Re: [RFC][PATCH] docs: note exception for PCIe IO port access
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From: |
Gerd Hoffmann |
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Subject: |
Re: [RFC][PATCH] docs: note exception for PCIe IO port access |
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Date: |
Thu, 9 Jun 2022 10:41:42 +0200 |
Hi,
> I find this too general; a PCI Express device is supposed to work
> without IO resources. Graphics cards with legacy VGA compatibility are
> the exception AIUI (see again Alex's blog about VGA arbitration), so we
> should spell that out.
Yes, it's an exception specifically for VGA ports. Can be turned on and
off here ...
$ sudo lspci -vvs00:1b.0 | grep BridgeCtl
BridgeCtl: Parity- SERR+ NoISA- VGA- VGA16+ MAbort- >Reset- FastB2B-
^^^^^^^^^^^
... and this is what vgaarb uses to route vga register access to devices
behind pci bridges.
take care,
Gerd