linux-kernel - Re: [PATCH 1/4] Documentation: arm: [U]EFI runtime services

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Message-ID: <20130626193158.GF9078@rocoto.smurfnet.nu>
Date:	Wed, 26 Jun 2013 21:31:58 +0200
From:	Leif Lindholm <leif.lindholm@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-efi@...r.kernel.org,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, matt.fleming@...el.com
Subject: Re: [PATCH 1/4] Documentation: arm: [U]EFI runtime services

On Wed, Jun 26, 2013 at 12:32:30PM -0600, Stephen Warren wrote:
> >> What about ARMv8? Is the intention to have a separate definition for the
> >> UEFI bindings on ARMv8, so that compatibility isn't an issue? What if a
> >> future version of UEFI allows LPAE usage?
> > 
> > It is unlikely that will happen on v7 since newer versions of UEFI are
> > expected to remain backwards compatible with the current spec.
> 
> The expectation of backwards-compatibility sounds nice, but it seems a
> little dangerous to outright rely on it.
> 
> Even if not a regular compatible property, can we define a property that
> indicates the UEFI revision or revision of this DT binding, so that if
> we ever have to change it, there is some way of explicitly indicating
> which exact schema the DT corresponds to, rather than having to
> reverse-engineer it from the set of properties that "just happen" to be
> present in DT?
>
> This is rather like the firmware node discussion that happened recently,
> where we were expecting to represent a firmware (secure mode) interface
> by a DT node, which would have a compatible value, which in turn would
> convey information about which "OS" the secure firmware was running, and
> well as any potential SoC-/OEM-/board-specific interface provided by it.
> 
> And who knows, what if UEFI gets replaced someday; presumably we'd want
> some way of explicitly stating "running under UEFI" vs. "running under
> something else"?

To me, these concerns are all covered by the existence of the
efi-system-table node, and the version number that you can extract
from the table (mandatory in any UEFI implementation) located at that
address. There is no reverse-engineering involved.

/
    Leif
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