linux-kernel - Re: Special handling of display/VGA devices in hotplug drivers

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Date:	Thu, 11 Dec 2014 22:57:18 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dely Sy <dely.l.sy@...el.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Rajat Jain <rajatxjain@...il.com>,
	Guenter Roeck <groeck@...iper.net>,
	Kristen Carlson Accardi <kristen.c.accardi@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Praveen Kalamegham <praveen@...tio.com>
Subject: Re: Special handling of display/VGA devices in hotplug drivers

> >> The PCI spec said that you were not allowed to hotplug VGA drivers.
> >> The big issue is that POST usually needs to run on those things, and
> >> there is no way to POST a PCI hotplugged device.
> 
> I don't think this is a problem any more, is it?  I think X can
> execute option ROMs, and if we assign the guest to a VM, the guest
> BIOS can also do it.

Providing the legacy I/O is routed to that device, it doesn't use DMA and
a few other things. X has been able to POST cards with vm86 or the 8086
emulator stuff for a long time (it had to in order to use most PC cards on
non x86 boxes).

Your bigger problem is the marvellous reliable way that X handles a GPU
simply vanishing, especially a legacy one.

Alan
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