linux-kernel - Re: [Xen-devel] [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters

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Date:	Thu, 10 Sep 2015 14:30:30 +0100
From:	Ian Campbell <ian.campbell@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	Mark Rutland <mark.rutland@....com>,
	"julien.grall@...rix.com" <julien.grall@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"freebsd-arm@...ebsd.org" <freebsd-arm@...ebsd.org>,
	"peter.huangpeng@...wei.com" <peter.huangpeng@...wei.com>,
	Shannon Zhao <zhaoshenglong@...wei.com>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"leif.lindholm@...aro.org" <leif.lindholm@...aro.org>,
	"shannon.zhao@...aro.org" <shannon.zhao@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"daniel.kiper@...cle.com" <daniel.kiper@...cle.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] efi/libstub/fdt: Standardize the names of
 EFI stub parameters

On Thu, 2015-09-10 at 07:08 -0600, Jan Beulich wrote:
> > > > On 10.09.15 at 14:58, <ian.campbell@...rix.com> wrote:
> > On Thu, 2015-09-10 at 13:15 +0100, Mark Rutland wrote:
> > 
> > > > In any case this should be separate from the shim ABI discussion.
> > > 
> > > I disagree; I think this is very much relevant to the ABI discussion.
> > > That's not to say that I insist on a particular approach, but I think
> > > that they need to be considered together.
> > 
> > Taking a step back, the reason for using the EFI stub parameters is
> > only
> > (AFAIK) in order to be able to locate the ACPI RDSP (the root table
> > pointer), which as it happens is normally passed via one of the EFI
> > firmware tables.
> > 
> > If there was a way to achieve that goal (i.e. another way to find the
> > RSDP)
> > without opening the can of UEFI worms then we could consider that
> > opiton
> > too.
> > 
> > a way != the legacy x86 thing of scanning low memory of the signature,
> > of
> > course.
> 
> But even x86 doesn't do that (other than as a fallback) on EFI.

Indeed, I was referring legacy (non-EFI) mode.

>  The
> configuration table is available to Dom0 (via XENPF_firmware_info:
> XEN_FW_EFI_INFO:XEN_FW_EFI_CONFIG_TABLE).

Under ARM we find out we are running under Xen from the ACPI tables, so
there is a chicken and egg situation there.

Not insoluble I'm sure, if we want to go down this route.
Ian.
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