Re: HVMLite / PVHv2 - using x86 EFI boot entry

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: "Matt Fleming" <matt@codeblueprint.co.uk>,
	jeffm@suse.com, "Michael Chang" <MChang@suse.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Jim Fehlig" <jfehlig@suse.com>,
	"Jan Beulich" <JBeulich@suse.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Daniel Kiper" <daniel.kiper@oracle.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Takashi Iwai" <tiwai@suse.de>,
	"Vojtěch Pavlík" <vojtech@suse.cz>, "Gary Lin" <GLin@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	"Jeffrey Cheung" <JCheung@suse.com>,
	"Juergen Gross" <jgross@suse.com>,
	"Stefano Stabellini" <stefano.stabellini@eu.citrix.com>,
	"Julien Grall" <julien.grall@linaro.org>,
	"George Dunlap" <george.dunlap@citrix.com>,
	joeyli <jlee@suse.com>, "Borislav Petkov" <bp@alien8.de>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Charles Arndol" <carnold@suse.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>
Subject: Re: HVMLite / PVHv2 - using x86 EFI boot entry
Date: Wed, 13 Apr 2016 12:25:03 +0200	[thread overview]
Message-ID: <20160413102156.b4qwhwbqvnnpmxgw__13496.918421197$1460543192$gmane$org@mac> (raw)
In-Reply-To: <20160412221225.GN1990@wotan.suse.de>

On Wed, Apr 13, 2016 at 12:12:25AM +0200, Luis R. Rodriguez wrote:
[...]
> Also, x86 does have a history of short DT use. Just pointing that its there as
> an option as well. I'll Cc you on some thread about that.

I don't see how this is relevant to the conversation that's going on:

How many x86 hardware provide DT? I bet this is 0%.

How many OSes can boot on x86 using DT? Linux maybe, certainly FreeBSD, 
Windows or OpenBSD won't be able to boot at all when provided a DT on x86.

Is Xen going to craft a DT for x86 based on ACPI? No, because it can't parse 
the DSDT or other dynamic tables that contain the information about 
the devices in the system.

I would also like to point out that DT or not DT is not really the problem 
here, the issue that George was trying to point out is that on x86 there's 
some legacy hardware that's considered to be always there, so it's presence 
is not signaled by ACPI, and HVMlite is _not_ emulating this hardware. It 
doesn't matter if the hardware description comes from ACPI or DT, this 
hardware is considered to be always present on PC compatible hardware.

Roger.

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